Birth control

I'm trying to get on the pill to help protect from pregnancy even though I don't have sex often but I don't know how to ask my mom for it. I'm only 17 so I can't go to the doctor and get it myself. I want my mom to know because she always seems to find out everything. She knows I've had sex and she told me that if I was going to continue to have sex she would put me on the pill but I feel weird asking her for it for that reason so does anyone know a good way to ask?