Pregnancy?

So I'm getting worried because I should have started my period 3 days ago and I haven't yet. I've had unprotected sex twice since my last period (and other times with a condom) but he's never came in me. What should I do? I feel like I'm going to come on like I have that kind of pain in my stomach and I'm getting headaches like when I'm on but I've been like this since Friday and now it's Monday. Do you think I will come on? Should I take a test? I'm only 16 and i don't want to be pregnant.