Ejaculated inside, lower abdominal pains, frequent urination.

I've been with the same guy for 14 months, have been having sex with him a week longer than that. We're both 20. I was on birth control, and that was our only method. He doesn't pull out, he just goes inside me without a condom. I got off the pill 9 months ago and he never stopped ejaculating inside me. Miraculously, I haven't gotten pregnant. I had my period last week, but it was six days late and my cramps were AWFUL, even worse than they usually are and I had terrible headaches. We had sex my last day on my period, the day after and the day after that. This is a very common thing for us. However, now I'm feeling lower abdominal pains in the same place I would have menstrual cramps. It's a mostly constant but very slight pain but hurts more when I stretch or move certain ways. I've also been very fatigued. Anyone know what could be causing this?