Im so insecure? Advice please?

[Eli]

Theres always this voice inside of me telling me that something else is wrong with me. Whether its how I look, what grades I got, how popular I am etc.. Im just such an insecure and unconfident person and its eating me up inside. Im just hurting so bad over it. I get insecure when I see a girl my age look pretty. For example : A girl on Facebook posted a new profile pic and got like 95 likes and she looks really good in it but the only things going through my head are that Im ugly, that all the guys will like her .... It even bothers me more since this girl used to be mean to me in junior high. I know Im not ugly, Im a little above average I guess.. A lot of people tell me Im "pretty" or "gorgeous" but no matter how many people say it, I don't feel that way. I just feel so insecure and ugly and its affecting me so much. How can I boost my self-esteem? Should I just face the fact that Ill never be as pretty? Its just affecting me and my confidence. Its bad enough that Im really not a confident person but now I have this too. It really bothers me. Any suggestions?