15 reasons of fatigue are:

1. Not Enough Sleep
2. Sleep Apnea [2]
3. Not Enough Fuel
4. Anemia
5. Depression
6. Hypothyroidism
7. Caffeine Overload
8. Hidden UTI
9. Diabetes
10. Dehydration
11. Heart Disease
12. Shift Work Sleep Disorder

13. Food Allergies

    Some doctors believe hidden food allergies can make you sleepy. If your fatigue intensifies after meals, you could have a mild intolerance to something you're eating -- not enough to cause itching or hives, just enough to make you tired.

14. CFS and Fibromyalgia

15. Mild Fatigue

    If you have mild fatigue that isn't linked to any medical condition, the solution may be exercise.

— Sleep Disorders - Fatigue Causes and Remedies.

[2] : Note that sleep apnea is any breathing disruption related sleep problem, such as due to excessive weight, aging, or allergies.

As others have said fatigue can have a lot of causes. But I'll outline some general things which I think most people would benefit from:

• Improving sleep quantity and quality. I recommend at least 8hours of sleep (for most people) and getting most of your sleep during night time. The latest you want to sleep is around 10-11pm in my experience, much earlier if you have to wake up really early.

You also can improve sleep quality by:

• Calming down before sleep by switching to more relaxing activities. Such as reading/taking a shower/stretching/meditation.

• Avoid bright light before bed. If you work on electronic devices you want to turn down the brightness/install a program like f.lux.

• Look into supplements/herbs that help sleep. I personally take 3-6mgs of melatonin every night and it helps me get to sleep quicker and on time.

• Avoid caffeine/alcohol before bed.

  • Eat at a caloric maintenance if you want to maintain weight. Otherwise do a slight deficit (~500 calories per day). Also make sure to eat a balanced diet (something like 40/30/30 of carb/protein/fat) from whole, natural foods and eat vegetables with every meal.

  • Make sure to hydrate all day long. Keep a water bottle and just drink from it all day.

  • When you start to feel lethargic. Stop what you are doing and do some kind of physical activity. One thing that helped me in the past was setting up an impromptu standing desk whenever I started getting tired. Walks also would help a lot. Scheduling like 2 x 30-40 minute walks a day, one earlier and one later in the day should help too.

  • Make sure you aren't being overworked/getting stressed. Manage your time and resources so that you are efficient with your work and you actually get things done. Don't overload yourself. Find ways to de-stress/take breaks from work.

Really a lot of it is being introspective and investigating why things are the way they are. Often times all you have to do is keep a log/journal and patterns will start to emerge to why you are behaving the way you are.

Further Reading

• How to increase energy levels and motivation
• Developing the perfect morning ritual
• More on melatonin

The amount of sleep needed for a person seems to be very individual, so the absolute duration of your sleeping time (7 h) will be difficult to discuss here, IMHO.

I recently read an article stating that the "built-in biorhythm" can not be changed, which is especially hard for people working in changing shifts.

Concerning your 7 hours: "But I am always sleepy" says that you think 7h should be enough.

• Are you sure?
• Did you try sleeping longer at night?
• Do you wake up yourself in the morning (after 7h), or do you need an alarm clock to get up?

There might be other reasons for a general sleepyness like

• nutrition
  • quality, quantity
  • check your eating habits e.g. last meal time & quantity vs. bedtime
• stress / burn out
• illness

recently I stumbled over an interesting article Tired of being tired (Leo Babauta) which covers the topic and some easy solutions

I've had this problem since pretty much forever, and the standard answers were all the things the people above have posted.

Maybe those answers apply to most cases, I don't know. All I know is that it didn't resonate with me.

Only a few weeks ago, I found these two article by the same author:

http://www.humbledmba.com/why-entrepreneurs-cant-sleep

http://www.humbledmba.com/become-a-morning-person-how-to-end-insomnia-f

Everything in these articles struck a cord. I said "YES - That's me". I haven't implemented any of the advice in this because thankfully my current lifestyle allows me to wake late and work late, but it helps to understand the many problems I had while in "standard" jobs over the last few years.

Maybe this doesn't apply to you, but most people don't seem to know about it, so hopefully it will be helpful for someone.

Something that nobody has mentioned is the possibility of ADHD. Specifically, ADHD-Predominantly Inattentive "Sluggish Cognitive Tempo".

This is a new diagnosis of ADHD that lacks the hyperactivity component often seen in ADHD children. You mentioned lacking focus and always being tired.

Check out the Wikipedia for it: http://en.wikipedia.org/wiki/Sluggish_cognitive_tempo

Here's a sample, see if this identifies you:

those with SCT are drifting, introspective and daydreamy, and feel as if "in the fog" (although in excited states, an SCT patient behaves very similarly to a traditional ADHD patient). They also don't have the same risk factors and outcomes. A key behavioral characteristic of those with SCT symptoms is that they are more likely to appear to be lacking motivation. They lack energy to deal with mundane tasks and will consequently seek things that are mentally stimulating because of their underaroused state, an intense craving for emotional and intellectual stimulation. Those with SCT symptoms show a qualitatively different kind of attention deficit that is more typical of a true information input-output problem, such as memory retrieval and active working memory, and display a wavering "up and down" mental pattern with extremely variable levels of intense thought, hyperactivity, failing memory, and sexual appetite.

It's worth mentioning because there are a lot of undiagnosed ADHD adults out there and not a lot of information as it's still a disorder being actively researched and understood.

Copied from a similar question I answered on the fitness SE:

You mentioned being tired during the day, does this happen even when you are getting enough sleep? You could have sleep apnea, a condition which causes you to stop breathing in your sleep. Sleep apnea constantly goes undiagnosed because sufferers don't realize that it is not normal to be tired during the day.

I started treatment for sleep apnea earlier this year and I cam say with no exaggeration that it has been life changing. No more falling asleep behind the wheel, no more afternoon fatigue, etc. I don't know if this is common, but I've also had an easier time falling asleep since starting treatment.

Contrary to popular belief, you do not need to be overweight to have sleep apnea, although it could be a sign. Sleep apnea tends to cause weight gain just as much as weight gain will cause sleep apnea. If you have a history of depression, snore, or if you are a mouth breather, these are also strong indicators.

If you have a significant other ask them to pay attention to your breathing patterns, if not ask your doctor to do a sleep study. They're usually conducted in hotels, it's easy, comfortable, and won't interrupt your schedule (you'd be in bed either way). When I did mine it was right next to the office, so I got to avoid the morning traffic.

If there is a qualitative (as opposed to quantitative) difference between your tiredness during the day when getting 7 hours/night and how you feel when you haven't gotten enough sleep, this is a strong indicator as well. Talk to your doctor, most sleep conditions can be managed and your quality of life will improve drastically.

I help myself with software + hardware. If You have Android device You should try "Sleep as an Droid":

Sleep as an Droid is an Android alarm clock with integrated sleep cycle tracker for waking you up gently in your light sleep cycle. Common alarm clocks ignore your sleep cycles, they wake you on schedule no matter your are currently in your deep sleep. Waking-up from the deep sleep is very unpleasant, it makes you tired and it may negatively affect your productivity during the whole day.

In contrast Sleep as an Droid tracks your sleep during night and given a time range, it chooses the optimal moment to wake you up (ideally in light sleep). Waking up in light sleep is natural, gentle and it may only be compared to the experience of waking up without any alarm clock.

You can test it for 2 weeks for free. After that it cost 1 Euro. It works fine for me.

Official Page for Sleep as an Droid

If You don't have Android device You could also buy Sleeptracker but it looks quite expensive and I didn't tested it.

I highly recommend reading this well researched article on sleep: http://www.supermemo.com/articles/sleep.htm

One important point it offers for you: Kill the alarm clock! It is highly detrimental to sleep quality/benefit.

Go to bed early enough so that you will wake up well rested by yourself before the time you would have your alarm go off. Keep that rhythm.

Here is advice on first building the habit of getting up at the same time every day: http://www.stevepavlina.com/blog/2005/05/how-to-become-an-early-riser/
The author first uses an alarm clock but says it is not needed anymore after some time, when you're sufficiently entrained to your regular getting-up time.

I wish you success!

"Diagnosis"

Most likely you have something called "delayed sleep phase disorder/syndrome".

This refer to that your "sleeping point" (nadir, part of the circadian rhythm) is out of phase, ie. in another point of the day than during your sleep. This is important as if you don't get "through" this sleeping point you will never feel rested no matter how much you sleep at other times. Usually people wake up naturally a couple of hours after this point - during the point you would feel a bit colder, and very tired if you stayed awake instead. This is a typical experience for night-shift workers.

People suffering for this are often categorized as B-persons (not to be confused with Type B personality), persons with a biological clock longer than 24 hours. Now, most people have a biological clock of 25 hours, but this one hour is too small to cause any problems for most.

Treatment

The way to treat this is by light-therapy and/or chronotherapy, as well as the use of melatonin tablets, to adjust the nadir/sleeping-point.