I'd honestly suggest learning how to meditate. You don't need to be religious (but you can be I guess) to do this. It will help get away from negative thoughts and clear your mind. It has helped me immensely with other things in my life, especially since it helps separate you from your ego.

The other thing I like to do when I feel down like you seem to be is to completely change how I look/dress. You can get a new hairstyle (which can really change your perspective) and clothing style and it can completely disrupt not only your own idea of how you look and feel about yourself, but other people's too.

Lastly, if you have tried these things and are still unable to reconcile how you look with your own idea of what you should look like, that is a real medical disorder and you should immediately seek a professional psychiatrist's help. The same thing that causes people with gender dismorphia to feel the way they do, as well as those people you've seen addicted to plastic surgery, is all caused by this. Although little is known about what causes people to feel this way still, there is a lot of help available, especially in the last 10-20 years or so. You should definitely seek out someone who specializes in body dismorphia. Even if you do not have this disorder, a therapist of some kind would be extremely helpful in getting you to a better place to feel about yourself.