4 weeks post partum large clot

I had my baby prematurely at 24 weeks on August 6th. He sadly passed away so I have not been breast feeding. The bleeding tapered off and was very light from week 2-3 and was mostly discharge. Near the end of week 3 it turned to brown spotting which I read could be the start of my period. Then on August 31st I woke up and it was bright red and resembled my normal period so I assumed I had started my period.

It has been 4 days since I assumed I started my period, I have had some cramping but not horrible so I wasn’t concerned. But I just woke up at midnight to take my dog out and when I was coming back to bed I felt a large clot come out of me. When I sat on the toilet I felt another large clot come out of me but I couldn’t see it because the toilet was full of blood. I passed another 4 or 5 smaller clots while on the toilet. I changed my pad and have gone back to bed. But I am very worried. I was officially 4 weeks pp yesterday.

I had an ultrasound on Sept 1st to check for retained product and there was nothing there.

I have read that your first period can be very heavy and have lots of clots. Is this normal. I need reassurance.