Birth control advice needed

So ive never been on birth control, but i know that at my 6 week appointment my doc is going to bring it up and expect me to go on one. Im fairly hesitant to do so, because I've heard alot of negative things about it messing with your hormones and weight. Im pretty sensitive to this because for the past 6 years ive struggled to get to a good place emotionally and physically (im in recovery from anorexia). Im really scared to start taking anything that might mess with my mood, or weight because i was on meds a while ago that made me gain alot of weight and that triggered a major relapse in my eating disorder and i cannot have that now with my daughter. I also know that every birth control effects everyone different, but im not really willing to start playing roulette with that kind of stuff right now. I also know for a fact i wont be having sex for a long while, so i really dont see why it would be necessary, especially if it could have such negative consequences on my mental health. But i feel like my doctor is really going to push it, because im 19 and a single mom, basically exactly the person they dont want having any more babies lol. And i know anyone can think they wont be having sex but then it "just happens", but i really do know for a fact that that wont be me for reasons im not going to go into on here. My question is is has anyone declined birth control at the 6 week and how did that go with the ob?