You feel worth something only when you're making other people happy. Usually this is not something to worry about, but in your case it looks to be affecting your life in a negative way. You may want to seek therapy for this as it may get worse. There are deep rooted "issues" that turned you into a helper, so to speak, and it will do you good to figure them out so you can understand yourself more.
I don't think it's normal, and unfortunately there are always opportunists ready to take advantage. You should feel you are kind, and that's very important but that should be balanced out with your own needs. I think you would benefit from some therapy so they could role play setting boundaries with others so you don't get hurt so often. Hugs!
You're a nice guy. No problem there.