Period like cramping after orgasm?

Is it normal to have cramping moderately like period cramping after an orgasm? Today is one of my high fertility days. Cycle day 15. My Clearblue advanced digital opk that detects two hormones gave me my first flashing :-) today, it should be the first of four days of fertility. I'm cramping within minutes after orgasm, it's been an hour and it hasn't stopped yet. Is this normal? I don't remember ever having cramping after an orgasm before.