depo shot and no period after stopping using it

I'm 16 and I had been on the depo shot for about 9 months. I had stopped using it and I still haven't gotten my period 2 months later. I stopped using in February2012 and it is now may2012. I'm not feeling sick, I have to per all the time, I've always had back problems and I've had a headache for about 3 weeks. My boyfriend and I have had unprotected sex since my depo ran out but I'm unsure someone please help