Post partum period?

I'm just curious to see what everyone else is experiencing.

This is my second period (3 months postpartum, exclusively breastfeeding)

Last month, my period was pretty normal in comparison to before I got pregnant. It was a little lighter and lasted a day or two longer.

This month, it has been weird! I've been spotting off and on for the last 7 days and this evening I've started bleeding heavily, passed two large clots about the size of my thumb, and am having cramps that are painful enough for me to breathe through, almost as if I'm in labor.

What gives? Is anyone else experiencing the same thing? Should I be worried?