How to i become unselfconcious of the way i look?

i dont feel comfortable doing anything anymore because of the way i look. i dont kiss boys because im worried what theyll think. i dont go to many social things because i worry what people will think of my appearance. i dont have a myspace,facebook,etc because i feel too bad about myself to put a picture and tihngs on it. im just having a hard time with being myself because i dont wanna get put down. can u help me or atleast give me some advice? no rude commentsss. youve been warned..