Pregnant ??

Ok so I had unprotected sex on Feb 21, about 3-5 days before my expected period. He did not come inside me, and we were in the shower (with water running). Now I am a week and 1/2 late on my period (supposed to have come Feb 23-24) and it's been about 2 weeks since the incident. I've taken 2 pregnancy tests but they were both negative. Also, right around when I was supposed to get my period, I spotted very lightly for about 2-3 days. Is this implantation bleeding? Am I pregnant? Should I retest? Please help! I'm only 19......