Low self esteem since i was a little girl

I've always wanted to know why I've had a low self esteem... People are always telling me that I'm beautiful and gorgeous and of course I say thank you but in the inside I just feel like telling them no I'm not why would you lie to me...my SO also calls me all these nice names.....but idk why I just can't accept my self.....I'm not going to lie there's times when I feel beautiful and I take pictures but that's really rare...and I always see other girls who are so confident and I just wish I was that confident but it troubles me sometimes i cry my self to sleep thinking why cant i just be as confident as every other girl i know.....another thing is i get so jealous if i see a pretty girl even in the presence of my SO....crazy right.....cuz then ill know for a fact that he will look in her direction and be like hey shes gorgeous ....in his head obviously... I've tried everything and nothing seems to help can someone help please....