Scared that I might be pregnant

I'm 16 and about 3 week ago I had sex with my boyfriend. We used a condom but it broke during intercourse and though he pulled out 2min later when he realised it broke, we're not sure if he pre-came in me or not. Over the past 2 weeks I've been having daily headaches that just won't go away no matter how many headache pills I take and recently I've been experiancing lower back pain and lower abdominl pain, however, it's just for a short time and then it's gone again. Also I've been feeling nauseous at times but I don't think it could be morning sickness... I had my period a week after having intercourse but it was 10 days early. I'm not sure if I could be pregnant or not... PLEASE HELP!!!!