hey, im almost in the same situation! well im 18 and already had a GF... but she picked me
well, i understand, but YOU CAN CHANGE!!! man, i am changing right now. ok let's get this straight. first, you need to get pretty clothes, i mean not like sport clothes or skate clothes. I mean clothes with style and that fits you well. it will boost you're confidence.
after that, its in the head. now that you're confident and good looking (and have good breath

) you must read and watch the most possible about PUA stuff, and social stuff. i mean pua isnt just a game, its talking with people!
ok then (i am at this point) you try on the field. you dont care about rejection, you use it to perform better next time. you must try your pick up lines, try some of canned stuff, practice kino (so it appears natural when you talk) and be talkative and social, and have FUN!!!
ok thats it, im gonna tell you how i do. cuz i almost live what you live. lets be strong!