Lenneh, you sweet thing, I wasn't going to comment on this because I don't feel qualified, and there are people on here much wiser than me, but I am lying awake thinking about this thread and I had to reach out.
Everyone has the voice telling them they are useless etc... you learn to squash it down. People who don't have that voice are usually massive arseholes.
As many people have said before me, you are special and perfect as you are. There is no such thing as 'normal', it's an illusion.
Being a teenager is a hugely confusing and painful time. I PROMISE it gets easier. You start to find yourself and become comfortable with who you are.
You have so much ahead of you OP. This time next year you will look back on this and feel sorry for the lost soul you were and wish you could go back in time and give yourself a hug. Your life is waiting for you, and you deserve it - it's yours!
To me you sound wonderful and sensitive. The world needs people like you, who feel deeply and who care. You must NOT surround yourself with people who do not see your beauty and value you. The world, unfortunately, contains people who will try to bring you down and break you, everyone comes up against them, the reasons they are motivated to do this are internal and nothing to do with you. You will never really know what the reasons are and nor should you care.
Go back to school and hold your head up and give the world a smile. I can promise you (as someone more than twice your age 
) our world is all the better for having you in it.