Don't give, to only expect something in return. People will always fail with our expectation of them. You have a big heart, that is why you give, And with a big heart, it can easily be broken. Don't change who you are because of others. Do things that make you feel good about yourself. Don't worry about what others think, or what others say, or what others do. You do need to stick up for yourself, and not get walked on or taken advantage of. Do it for yourself. It will make you a better person
I'm sorry you are feeling this way and hope it will pass. Many women I know went through something similar around age 24-25 and wanted to reinvent themselves. I hope you come through it ok.
It is important not to loose yourself in the service of others. Keep things in balance and remember to take 'you time.' It is more important than some people think. If you are selfless all the time, you just burn out.
Good for you!