missed period

I'm on day 37 of my cycle, my period is late by 7 days, I took a pregnancy test 5 days ago and it says that I'm not pregnant but I still haven't gotten my period and I'm really nervous!!! I've been kind of stressed the last month but only missed my period because of stress one time before but that was a while ago. I've been having sex but we've always used condoms and he doesn't always finish, but the last time we did it was Dec 12 and he finished, but my period was due the 14th so I don't think I was fertile?? The time before that was Nov. 24th but he didn't finish that time so I don't think I could be pregnant from that? We always use condoms but other than that I don't use any other birth control. I'm nervous. do you think it could just be me missing it because of stress or do you think it might be something more? I'm 17 and in my senior year of HS and I DO NOT need a baby AT THIS TIME IN MY LIFE. Please I need reassurance and someone to talk to.