Two good answers already, but they won't solve your problem. What you need is a tracking system. If you already have one, then in fact your hard work IS visible (unless you're not utilising it). If you don't, use one, make one, find one. A lot of people see a tracking system and constantly keeping it updated as a chore, I don't, it's a tool, incredibly useful if used properly.
You should be documenting each change requested in a project, getting signed off multiple times along the way to completion by the client and your superiors. Any clarifications additions or pretty much anything else should be documented and available. Both for your purpose and for a host of other reasons including extremely important things like dispute resolutions and client negotiations.
Any changes a client requests should be going through the manager for approval before you start actioning them, if they aren't you should be informing your manager each time via email at least and getting approval. You shouldn't be the clients first point of contact, but if you are, ensure your manager is cc'd on everything.
Scope creep is not your problem, you can only do something about it indirectly and protect yourself from it impacting on you professionally. Your manager, project manager etc,. are supposed to deal with it.