HELP ME PLEASE

Beth
My mom is very strict and very suspicious. And I am dating a junior (I'm a freshman) we have been together for 8 months and recently my periods have become long and TERRIBLE!! My cramps are so bad to the point I started crying last night. I want to go on birth control but my mom will think I want or for other obvious reasons! I asked her once a year ago and she said its bad for me, any advice ?