cramping 2-3 DPO

Jessica
So I'm not sure when I ovulated this month I was so regular for the last few months that I stopped testing ovulation. I have had really bad cramps today in my lower abdomen and in my lower back. So I took an OPK test and a pregnancy test. I am on cd 17 and 2-3 post ovulation. Any ideas on why I'm cramping so bad mid cycle?