How do you gain self confidence?

I'm 22 and I have no self confidence. I'm constantly worried about what others will think of me and I'm not even in highschool anymore I shouldn't still feel this way. I'm waay to sensitive. When I go out in public I'm always worried I'm gonna run into somebody from my past and they are gonna see how fat I've become or that they will some how find out that I'm not doing much with my life. I'm always worried about meeting new people too because I don't want tthem to pick up on how I'm socially awkward and I just have the fear of rejection. When im. Around people and try to talk I fumbIe my words because I'm so nervous my mind goes blank and I don't know what to say.i feel this way around my closest freinds too. How do I love myself? I've tryed telling myself but I just don't believe it its not helping. What do I do?