How To Enhance Breast Size?

Im 16 going on 17 i weigh about 123lbs and im about 5'5 or 5'6. i started my period when i was about 11 and i barley fit in a 32a :( my moms boobs aren't that big either but my older sister for some reason has really big boobs. I've been thinking about going on birth control but im not sexually active or plan on being anytime soon! Can going on birth control for breast growth be dangerous? or is there anything else that will make them bigger?