Help :(

So Ive always been too scared to ask my mom to put my on birth control. I don’t want on it because I’m sexually active I need it because sometimes my periods last 14-17 days and my cramps make it hard to walk. Recently I asked her and she said yes :))) but now my friends are scaring me saying that I’m going to gain a bunch of weight due to me being skinny and that my face will break out and I’ll be super nauseous. Do I have anything to worry about?