My last period was Dec. 12th - Dec. 18th. I had unprotected sex on the 21rst. He used the pull out method. My period tracker says I ovulated on the 26th. Last night after sex my lower stomach started aching about and hour after sex. My boyfriend was playing around and hit me in my stomach where my uterus is, and I felt and odd aching feeling like something was going on in there. Could I be pregnant?