stop being so insecure

I’m so insecure about myself. I look at myself and I’m always worrying if I’m ugly or to fat. Do I really have to worry about this so much? I’m always saying sorry to my friends, family, and boyfriend and it drives them up the wall. I think this is the cause of my clingyness as well as saying sorry so much. If I get more confidence it would make the world so much better. I have not confidence in my abilites in math or school and I don’t trust my own opinion. I don’t trust that other people will like me and basicly I don’t respect myself in this sense. But how do I do better? How do I get confidence?