you are not worthless. never say that. you are an individual that has the potential to change the world. you have your own mind.. you're not a clone like so many people are. the only thing that could possibly make you worthless is giving up. never give up because tomorrow is always a mystery. never give up because you'll end up wondering what would have happened. there's endless possibilities in life and there's so much you have yet to experience.
you are worthy to know people. there's no reason you shouldn't let yourself have friends. i know for a fact that you're a really sweet person and i'm positive that you have a wonderful personality that you're hiding from everyone... including yourself. just remember that you're your own worst critic, and what other people think doesn't matter. once you know that, things will start getting easier. friends are nice to have, but they aren't necessary right now because you just need to get through school so you can have a wonderful future.
i do believe that erika is right. depression very well might be the cause of this. it's easily treated for many people, and the sooner you get help, the easier it is to get better.
if you want to talk you can PM me or IM me on aol/aim