What Causes Grey Clump Like Discharge During Menstruation?

Hello! I started bleeding dark brown blood the beginning of the week and had a Leep procedure the day after. My doctor noticed the blood and asked if i will be starting soon. My periods have always been irregular. anyways, i started to cramp and have back pains yesterday and today this morning when i went to use the bathroom, i passed a grey like clump. I was given a pregnancy test before my procedure but it was negative. Should i retest? Thank you