What could be the cause of constant cramping, not pregnant?

I had my first d&c about 5 months ago and I’ve had recurring miscarriages. Lately I’ve been having constant cramping and it’s really uncomfortable. I’ve been on the pill since the miscarriage but lately the cramps are just getting constant. Does anyone know what could be the cause? I’m not bleeding either and not near the placebo pills. I also took a pregnancy test just to be sure and I’m not pregnant. I’ve also had ultrasounds and they say everything looks fine.