Let me preface this by saying, I am pretty sure I had unprotected sex with my boyfriend around the time of ovulation. I say I am pretty sure because at the time I was a bit (read: really) intoxicated.

My periods always start exactly at the 28 day mark on a Friday in the morning, usually by 9 or 10 am. My period also normally gets heavy by the next Saturday, and the heavy flow usually lasts until Monday (day 4). My period then gets lighter, and ends by the end of the day on the following Thursday (day 7).

This month, it didn't start until Friday the 17th at 5 or 6 pm (doesn't seem like a big deal, but it ALWAYS starts in the morning). My period was only heavy Sunday and part of Monday, but then basically stopped on Tuesday. I've had little to no bleeding since Tuesday, barely enough to warrant a liner. 

Is it possible I could be pregnant, and this is messing with my period, or do you think it's just a random fluke that this period is so different?