i feel very bad about myself

I dont know if this is considered as TMI or not but I feel very bad and self conscious because i dont see myself beautiful or hot or other things, i was very fat few years ago and i still feel fat and ugly and i have a very low self esteem. everytime when i am somewhere i start to compare myself to other girls and everytime i see on social media fit girls that work in the gym i start to feel disappointen in my appearance even though i know that someone else beauty is not bringing mine down. Do you girl have any advice from me on how can i build confidence and grow my self esteem?