Can I get on birth control as a virgin?

Well my period sucks. I bleed for 7 days usually and heavy the whole time. I'm also going into highschool and my mom and sister want me to be protected. So today my mom called and asked the clinic if they could put me on a low dose birth control an they said that I had to be sexually active, would need a pap smear, and I was required to get the hpv shot. I plan to get the shot but this doesn't sound right to me, I mean isn't the point of birth control to prevent pregnancy? So why would you get on it after you've had sex not before? And my sister was my age and a virgin when she got on the pill.