i went through a phase thinking the exact same thing. it was only a few years ago,probably around your age actually.it was when i first started getting help.i thought that it was all some mistake,that i could have handled it by myself and now everything was getting worse.now ive relapsed (hurrah..) and im feeling the exact same thing AGAIN.."wth am i doing??!"
wish i could offer advice better than "hang in there" but i cant.i can offer you comfort that i know how you feel,and that as long as youre around here in PC you are definetly NOT alone