What you're saying right now is the story of my life. I'm 17 and I've been diagnosed by BDD. I can't go to school anymore, I ve lost all of my friends and I lately, I don't come out of the house anymore. It really has ruined my life. When people tell me that I am pretty, I will always think that they lie to me. On the other hand, I know that I'm not a monster, it's just what I see in the mirror.
But since a couple of months, I've been in a new therapy, and it looks like it's going to work. My therapist is on a vacation now, so now I'm not doing very well, but it has helped me before and I'm sure I'll be fine if we start again. This therapy is called EMDR and it seems very effective on BDD. Maybe you should go talk with a professional? Believe me, it will already feel better if someone tells you that you're not crazy, but that you really do have a disorder.
I hope this can help you a bit (and that you understand my Enlish, haha) and I wish you good luck.