Bloodless period with heavy cramps

Hi everyone, I’m a 32yo cis woman, I’ve had an IUD since my daughter was born eight years ago (this one is actually the third after I’ve had issues with previous ones). Since then I’ve not had a regular menstrual cycles, which I know is normal. But for a few months now I’ve had very short periods with just a bit of spotting. Now this month I’ve had a “normal” period, so far so fine. Ten days later I get my period again, this time with heavy bleeding, which I’ve not had since before the IUD. The bleeding stopped after four days but I kept having increasing cramps, to the point where it felt like when I was a teenager until I went on the pill, hurting so much I couldn’t move, cried from the pain, had muscle stiffness. What I find odd is still having such cramps for days while I’m not even bleeding anymore, which doesn’t seem to make sense to me. Has this ever happened to you or do you know what could cause this to happen? Thank you.