Intestinal bleeding on eating gluten.

I have prolapse hemorrhoid however last 2 decades I have been fine managing it by avoiding certain foods & eating more fiber. Last 1 year eating wheat products and certain grains I get IBS kind of symptoms & I start bleeding during bowel moments. On & off this keeps on happening, when I avoid gluten zero bleeding is noticed however food management is not healing it fully as after 2 weeks if I accidentally eat some gluten I again start bleeding with bright red blood with some tissue & mucus. So now symptoms are shifting from IBS to ulcerative Colitis since I have persistent diarrhoea. Which doctor should I consult? Is colonscopy needed to look into the intestinal walls & do biopsy if needed? Looking for advice. Thanks!