I can't change my looks. First off, you are probably exaggerating about your looks. Secondly, physical appearance is only part of attractiveness. The most important thing, though, is to stop rating your total self-worth on attractiveness. It sounds like you have a belief to the effect that to feel worthwhile, you must be attractive.
Attractiveness can be a desirable trait, but it is just one of many traits people have.
If you base your self-worth on attractiveness, you will be insecure no matter how attractive you are. I know many attractive women who feel insecure and down on themselves because they think they should be more attractive. Also, they are often afraid they won't keep their looks, so their self-esteem will go in the toilet. Most people are judged by appearance first, though. We have to love ourselves for who we are.