Birth Control

Okay so I need advice on how to tell my mom I want on birth control I just don’t know how. I’m not very comfortable explaining to her why I need things like tampons pads etc. I’m not sexually active, I’ve done research and everything I’m extremely under weight and I read it may help me gain weight while also protecting me from getting pregnant if I do ever have sex. I just need help on how to talk to her about this subject