What would cause cramping for 2 weeks leading up to expected period?

Right after ovulation, it was cervical cramping. After a few days, it became uterine cramping. Like my period is about to begin, only I'm not due for 3 more days. So it's been almost 2 weeks of cramping. I'd think it was pregnancy, except my husband had a vasectomy almost 3 years ago. What else, besides pregnancy, could cause extended uterine cramping? I usually only get it the day AFTER my period starts.