Got my BFP on 02/26! Now a question.....?

According to mymonthlycycles.com I was supposed to have ovualted February 19th. However I think it occured 02/16, a few days early. I tested on 02/26 and got a BFP! How is that possible? I wasnt due for AF until 03/05... So I would only now be approx. 3 1/2 wks and HPT shouldnt be showing up yet. (Ive taken 8...lol slightly obsessive!) Is it possible that I conceived last month? My period on 02/04 was shorter then normal only approx 3-4 days with a cpl days spotting. Also, Im already a little bloated&nauseaus. What do you think?