I've had sex but I can't tell my mum

So I'm 17. I want to get on birth control and I've talked to my mum about she said to wait until I'm 18 which is in June. 
The thing is I've had sex, almost a year ago now, I was 16 a month away from 17. It was with my boyfriend of 8 months at the time. We're still together and he's the love of my life. We're responsible and it took a lot for me to lose my virginity, we talked it over so much made sure I felt ready he did too (we were each other's first). This all feels so long ago now but my mum still thinks I haven't had sex. 
I know I should've told her but she makes it so hard. I've tried to bring it up multiple times talking about my friends and how they've done it or someone who's gotten on a form of contraception. And she always tell me I'm too young or not ready or I shouldn't be pressured. She's says the last one the most often. She always says not to give in to boys or when my friends boyfriend cheated on her (who she knew had had sex) she said see even if you put out you won't necessarily stay together. 
I have no idea how to make her understand that me and my boyfriend are responsible and we're for real and I want to do it with home and I wasn't pressured at all. I need som help or even a perspective of a mother maybe?