Mirena - cramping 8 months later...missed my period?

When I first got the Mirena I had cramping but then it stopped after about 6 weeks.

I’m 11 months postpartum and I got my period last month for the first time. This past month around the time my period was supposed to come it looked like I had very very light blood...almost pink looking. Not nearly enough to fill a pad.at first I thought it was the start of my period, but it just never came...unless that was it?

Now about a week or so later I’ve had some pain (more uncomfortable pain) under my pelvic bone..it’s tender to the touch. Right now I currently have cramping and slight lower back pain.

I took two tests and both were negative. Any thoughts what could be causing this? Is this normal?