I have been having blue bowel movements for past few days with severe stomach cramps and change in my bowel movements. what could be the cause?

IBS: I am not sure why you have been having blue bowel movements but your stomach cramps and change in bowel movements could be due to irritable bowel syndrome. If you have had any recent infections or if the pains worsen you should get evaluated by a physician.

Tricky: blue covers a wide area. Black would be typical for ulcer and with pain is a serious condition. It's hard to get blue. Prussian blue and methylene blue antidotes or other food dyes. Beets are blue-purple. sky blue is very unusual and would imply both a dye AND something that makes the stool pale (liver disease for example). Blue green isn't that unusual and can occur from vegetable matter.