Intense burn after BM 18 weeks post fistulotomy

Hi I had an intense burn after bm this morning. When checked, there is black dot on top of the scar and slit opening but no discharge. I am 18 weeks post fistulotomy. This is scary. Has anyone experienced this before? My CRS has told me to get second MRI and said it could just be a fissure and black spot could be blood clot or debris. I am so over this.