The pill?

How do I persuade my mum to let me go on the pill? I'm 16 and in a relationship so I want to use it as a birth control but if i told my mum I wanted to have sex I don't think she'd let me see my boyfriend a lot or let us be home alone. I also want to go on it to regulate my period and stop ovulation pains so I could use that as an exuse, any tips on asking her?