Missed Period and horrible cramps

First off i am going to start out by saying i am NOT sexually active there is no way that i could be pregnant and up until this point my period has been on time and regular every month. I have been having my period for 3 years. I haven't had a period in 4 months and i have sharp pains in my lower stomach area at least 3 times a week..What could this be. And what could i do for this. I haven't been to the doctor yet because the nearest one is 45 minutes away and I am 15 so i can't drive and i haven't told my grandma yet. Please help as much as possible