It sounds like you're projecting thoughts onto other people, which is rarely accurate and often harmful to yourself, as you've found with the self-sabotage. Stop worrying so much about what others think and turn those thoughts into ones of pride, and happiness over your progress.

I know it isn't easy, especially when you're young, but when you hear those thoughts start to sneak into your thoughts replace them with positive reinforcing ones.

Is it also the case that if they comment on your weight loss, that it verifies they had noticed you were fatter? Maybe that was something you had denied to yourself. Yes, you were fat. Yes, people noticed. Yes, you are thinner now. It is okay, 2/3rds of the population is overweight and it is something most of us struggle with. Changes in size happen.