self confidence is a very tricky thing, and it sucks because the only person who can really change it is you.
but there was a few things i did when i was self conscious that helped.
try going out and buying some nice new clothes that make you feel good, and just spend a day all to yourself and get ice-cream or something.
then have a day where you wear these new clothes and do your hair nice and do your makeup all pretty. dance around in your room to your favorite songs and go outside! i know it sounds stupid, but simply getting dressed up and feeling like you look great can make you feel great as well.
another tip: faking it. people always say 'fake it till you make it' which is actually pretty true. if you try to at least fake being confident, it will soon come in turn. don't degrade yourself or saying that you're shy, it'll get into your head that you really are. walk with your shoulders back and your chin up; it gives your body mentality a boost.
also this sounds REALLY stupid, but in the morning try listening to one of those stupid songs like "Boss Ass Bitch" or any rap song about being awesome. it's funny but it'll make you feel better.
Again, self confidence is a weird thing and there isn't really one way to become confident. start with small things, always go outside and do things instead of staying inside. it's a mentality thing so you really need to find a way that you can become confident in yourself. it'll take some time. i definitely suggest just faking it though because you really will become confident that way. good luck!