I have a serious question about my period?

So I'm 17 and have been getting my period since I was 13. My period has always been kinda irregular (every other month or every 2 months) but now I haven't gotten my period in 8 months. I had 3 spine surgeries in the last 3 years and that caused my periods to stop all together for a few months after. But my last surgery was in January if 2010 so I don't think it should still be bothering me. It was 6 months before I got my last period. Idk what to do. When I get my period its really heavy and I get super bad cramps and headaches. I'm still on a bunch of pain meds and muscle relaxers for my back and idk if that could have anything to do with it. It bothers me because I don't have a set date to get my period so it can show up at anytime. And I know there is absolutely no way I could be pregnant or have an STD because I am a virgin. My mom doesn't want to take me to the doctor because I'm her little girl and she "doesn't want my legs spread in stirrups." What would you do? Is there anything you recommend or what could be causing it? Even though I'm not having sex, would birth control help?