You have mentioned your periods have stopped when you were 15, how old are you now?? I can't answer your question directly but I can offer you this advice.
I would definitely get it checked out as there can be many things causing this. I was actually in the same boat you are in. I stopped getting my periods for quite a while when I was younger. It didn't bother me one bit but because it is not normal, I got it checked out. I was diagnosed with polycystic ovarian syndrome (pcos) which was causing the missed periods. I was given the birth control pill to make me regular. Sure enough, with the first pack, it worked. To this day, I am still taking the pill and have not missed a period since.
To be on the safe side, I would use a form of protection, if you decide to have sex, until you find out exactly if it is safe or not.
At the time it happened to me, I was a virgin, same as you, and it was not until I started the pill that I became active.