I think that it's very normal to feel self-pity. It's okay, but to move past it (for me) I have to do two things.
1) I have to just allow the feeling to happen for a bit. Sometimes I cry really hard, but then
2) I try to focus myself on something else and think about things I'm doing alright and things that are actually kind of okay about me.
It also helps to try to think about what you can do to fix whatever you feel bad about. Sometimes that can be difficult if it's physical, but if it's a personality thing then you can always try to improve it.