Birth control

I live wth my boyfriend I am 16 year old we have sex around almost every week so I desired to take birth control pills be I have heard that they can make u fat or later on they can make it difficult to have baby's I haven't started them yet I have them wth me idk if I should take them or not I also heard if u don't use a condom u can still get pregnant if u are on birth control what should I do please comment