Haven't started my period. 2 weeks late!

I just noticed last week that my period never came (usually starts around the 25th) and I was worried that I may be pregnant. I've missed periods because of stress before, but this is outrageous!! I've taken hpt and all of them come out immediately to be negative. I'm only 17 and I know for SURE that I cannot have any children, has this ever happened to anyone? I have been extremely stressed, but should it really be able to prolong my period by that much? me and my boyfriend didn't use contraception, but he's completely sure that I'm not pregnant where as I'm stressing out about it. Any advice??