Check with your doctor but it could be IBS or in the worst case the beginnings of colitis or something like that. If you're having pain, blood in the stool or anything like that it could be colitis. Ask your doctor about these possibilities as I am not a doctor, this is just based on my personal family history and colitis and IBS both exist in my family with similar symptoms. It could also be something as simple as diet, but make sure you check with your doctor.