I'm sorry you feel this way and I hope it's some consolation that most people feel this way at some point in their lives especially when they're young and trying to figure out their place in the world. If you were to honestly analyse yourself I'd bet there are things about yourself or that you've done or achieved that you are proud of or feel good about. Talk to someone professional if this feeling begins to be too much and takes over your life completely. In the meantime do things that make you feel good, raise money for a good cause, help a friend or indeed a stranger, achieve something- a goal even if it's a small one (to start with). Take care and stay strong!