Self-doubt is a killer. You would do well without it. The faster you can identify what they are specifically, the better. You know what they are. The things about yourself that make you feel small or less than. Do yourself a favour and find ways to fix them. Do not just sit there and do nothing about them. Of course, some things are fixable and some are not. Know the difference. For example, you will have quite a hard time changing your height but you definitely can do something about your weight. If acceptance is not on the cards yet, learn to accentuate the good and mask the bad. Seek external help, do some research in the library or the internet. Get educated and gain more knowledge in the area that is messing up your self-confidence. Work really hard to make them better. It might take a while but have patience. Just keep at it.