When you're that young cramps can be especially bad, because your body is still adjusting to everything. It sounds like you need to go to an ObGYN
and get prescribed a birth control, this will help control your hormones, and make your periods/cramps less intense and more predictable. This is common for girls who have bad cramps.
Besides that, when you have cramps (or know they will be coming) take a couple of ibuprofin, lay on your left side (if possible) and put a hot water bottle on your lower belly. It can also help to go to a Natural Foods store and get a PMS vitamin supplement, which will help with cramps. I still strongly suggest the birth control though. Good luck!