How to ask mom for birth control?

im almost 18 and my bf is 20. wei have been dating for 2 years. we havent had , because i was yung when we first started dating but i think im ready. i want to be responsible about it, and i truly do love him. and my mother really approves of him. i just dont want to freak her out..she doesnt have issues with the pill ( she is using it) but i just cant find the words to say it :( please help