Birth control

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So im 16, and sexually active with my boyfriend. I want to get on birth control, but I am so scared to approach my mom about it. She has mentioned before that I need it if im gonna be sexually active, but her and I arent close and i fear that she wont let me be around my boyfriend as much anymore. My dad told me to tell him if i am sexually active and i can get on birth control, but im just so scared. Any tips on how to approach parents about it? And how much is birth control most of the time? I also want it to see if it can help my insanely bad cramps, and possibly help me gain weight.