Miscarriage or something else?

Two weeks ago I passed this piece of tissue, ever since then I have been bleeding which has alternated between brown to dark red (which I suspected was my period), I have had possibly 5 counts of dull cramping (nothing excruciating, kinda like period cramps), one count I did have a few seconds of a sharp pain in uterus, the other day I passed a thick looking brown piece of tissue, I’ve passed a lot of small blood clots. I was on the pill, so I wasn’t trying to get pregnant so I was never sure if i was pregnant, but it’s a definitely a possibility as I had a regular partner.

I did stop taking the pill for two months when I wasn’t seeing my partner, and during that time I did not experience any morning sickness or pregnancy related symptoms (apart from tiredness? but i believe that’s due to stress)

I went to ER to get my bloods and urine checked, which came out fine. However, the doctors said that there is still a possibility, as those tests don’t constitute to a 100% possibility.