the most likely cause of these syomptoms is infection of colon
When did symptoms start? What is the color of the stool?
Most likely causes:
1. Lactose intolerance
2. Fructose malabsorption
3. Clostridium dificile overgrowth in the colon
4. Diverticulitis
5. Food poisoning with bacteria (problems usually go away within 5 days) or parasites, if problems started only recently.
Test for 5. (stool test) can be performed by your primary doctor. For 1. and 2. you can try lactose-free diet and low-fructose diet, each for 2 days.