Birth Control?

I'm 17 I'll be 18 in two months so I guess it really doesn't make that big of a difference. But I was pretty late getting my period, it didn't start until I was 16. And since then it hasn't become regular at all. My periods generally come about every 2 or 3 months with varying lengths and heaviness. I want to go on birth control to even everything out because I'm constantly worried that my period is going to come when I'm completely not expecting it. But also I'm in college now and I don't know it just feels like the right choice. Anyways my mom is completely against it and she keeps telling me that it causes cancer but from the research I've done, it looks like it might actually prevent ovarian cancer.  My mom is really anti chemicals and doesn't like the idea of putting unnatural hormones in my body. I don't see a problem with it. But like I said I'll be 18 in 2 months and then it's really out of her hands. I guess I just want your opinions on how I could convince her, or if you think she's right, why?