Cramps??

I had sex with my husband today BEFORE checking my app. Anyways, he didn't pull out and I'm not on birth control (I switched to the pill and keep forgetting to start it). When I checked my calendar it said I'm ovulating today and now I'm cramping really bad. Are the cramps just bc of ovulation lot what?? We also had sex like 3 days ago during my "fertile window" and he didn't pull out.