Ok, just so all of you will know you are able to get pregnant while you are having your period. It depends on when your body releases the egg. That can take place anytime, it DOES NOT DETERMINE WHEN YOU HAVE A PERIOD (that's how a lot of people get pregnant), because everyone body is different. Sperm can live in you body for up to 7 days, you are fertile for 48 hours from the time your body releases the egg. If you had sex before you period started, and you one of the people who ovulate while your period it on then yes, there is a possibility, and like some one said before "it could be from the implantation of the egg". You might want to wait till you next period is due to take a test. However, I can tell you that this had happen to me when I got pregnant with my daughter. I had a 'normal' period in january, but in february I had a short and light period. Come to think of it Valentine's Day was on that friday, and i went to florida b/c my period came on and messed up my weekend, but by sat it had went off. I was in the process of switching birth control b/c I was using the patch and it would come off b/c of my clothes. I went to the dr b/c i wanted to get the shot again, and the day my period was due (every 28 days like clock work) it didn't show, so i took a test from the dollar store (lol) and it came back positive. I can tell you that I only had sex right after my period went off in january. Hope this helps