Hi Kelly, yes, I had this leading right up to my first period, after the post partum bleeding slowed down, and the whole month between that and my second period. It stopped when my second period ended. I still ovulated though (was temping) and I got pregnant on the egg released after my second AF, so it didn't affect my fertility.
Doctors reckoned that I had a hormone imbalance, as they could see no retained products on a scan. They suggested I went on the pill to settle it down. (I didn't do this as I was convinced it would stop after second AF, which it did)
hope this helps
Xx