I've had left abdomen pain, occasional hard bowel movements and microscopic blood in stool. Now notice I have some small areas of black tar stool that I haven't yet told doctor. Her working differencal is IBS with diverticulitis. Is correct w/ tar?

Melena. Black tarry stool, otherwise known as melena, can sometimes be due to diverticulitis, but certainly can be a sign of bleeding in the upper digestive tract. You should share this new finding with your doctor and see if it affects her working differential. You may need tests to rule out an upper gastrointestinal source of bleeding. Good luck.