J.B.
Does it feel like crampy, uterine pain or like muscles or joints? I had pain right in the center of my pubic bone after my 2nd child. I waited several months to ask about it, went to PT for a while and it didn't get better, then finally had an x-ray and learned that I had bone inflammation at the pubic symphasis joint. It was treated with anti-inflammatory medication and I was better a month later.
There are lots of weird things that postpartum pain could be - I would start with your OB-Gyn and see what she or he says.