Depression

Why do I feel happy one minute and feel like dying the next. I feel like everyone in the world is against me. Why am I not pretty? How come nobody wont answer these questions? why cant anyone see that I am not normal? I think if they really cared, they would've found a way. I stopped caring completely. I walk in the street and I can at least one positive thing about everyone who passes by me. When I look in the mirror, I see nothing. There is not one thing that I like about myself at all. I mean its not fair that everybody out there is so great and so happy and no matter how hard I try, I can never find that inner peace. Sometimes i want to cross the street on a green light just so that a jumbo truck can crush me. I hate myself for reasons that are unknown even to me. why am I like this