Birth Control and Weight kiss

Hey, so I've been having really bad cramps my entire life. And my mom is thinking about putting me on birth control for them. Like, I'm only 15, but I've taken 5000 mg of pain medication for cramps in less than a day, and still had pain. But my mom told me that it causes people to gain weight. I'm already overweight, but it's manageable. But I don't want to get worse, and I definitely don't want to develop another eating disorder to lose weight. Does anyone have any tips that could help?