Scared of getting pregnant

My boyfriend and I have recently started having sex and we are 16. I'm not on the pill yet but I'm planning to get on it sometime in the next two weeks, so we have used a condom everytime. The thing that scares me is that I never get my period, the last time I had a proper period was in December and then I had a tiny bit of bleeding on the first of this month but it was gone after a day. I continuously have back aches and cramps so it's hard to tell when I'll actually am meant to get it. I have a huge fear of getting pregnant and I know I shouldn't be having sex if I'm scared but, what should I do? Is there any chance I could be pregnant?