femanon here, how do I deal with body dysmorphic disorder
People tell me I'm attractive but I stop feeling like I'm the worst looking girl ever
Well when guys are all mopey about their small dicks the first thing people say is "stop watching porn with guys in it" so you stop seeing unrealistic standards to compare yourself against. SO, do you look at naked women OP? Probably stop.
I had trouble with this until I moved out of my parents house. My mom would tell me I was getting chubby (I wear a size 3 in pants) and that I shouldn't get a big head because I wasn't pretty. If you're dealing with a situation like that just getting away from it will do amazing things for your confidence levels.
People have low standards. I've been told I'm handsome but I'm objectively not. I look disgusting. I know this because I've spent a great deal of time examining my features, the people paying these compliments have not. The same probably applies to your case, so I think you should trust yourself more than amateur opinions.
Honestly, the only way to overcome this is to have the stupid slapped out of you. Put a sign on your back that says "I'm retarded, please punch me" and walk around the ghetto for a while.