I need to reinvent myself..?

I'm really quiet and my quietness means that some people make fun of me at school and I just can't stand it any longer. I don't know how to break out of my shell though. I really need confidence and I just have no idea how to get it. I get so paranoid when I'm around everyone now. Like, if someone is laughing behind me, I'll automatically think they're talking about me and laughing at me and it's just horrible. What can I do?