I really don't know whats wrong

I don't know whats wrong with me, that is as simple as i can put it. My parents are ok, I have friends but i feel something inside gnawing away at me and whenever I am around people I usually feel like I have to force the smile so they won't ask me "are you ok" Little things bother me and I don't know if I can handle it any more the only thing that usually stops me from cutting is playing around with a soccer ball but sometimes thats not enough. I just don't know whats wrong with me why am I not happy I should be happy shouldn't I