I get that feeling, I've been told that it's referred pain from my uterus. It's similar to when I had a post partum infection and haemorrage after my other babies, it's really heavy and painful. My tummy didn't hurt then, but that area ached like hell.

I get it now and have most of the pregnancy if I squat or am sitting unsupported there, or for a good few hours after DTDing.

I'd definately mention it to your OOB due to your history especially.