My father is having bowl problems?

My dad lately has been having problems with his bowls. He hasn't really had diarrhea, but he's been having loose stools that are yellowish, a bit mucous-ey, and some white specks in it. He went to the doctor to ask about it. The doctor says that it isn't a viral/disease sort of thing... but he doesn't really know what it is. He also hasn't had any change in diet.Please help me! I hate to see my dad in this kind of situation. Do you know what he could have?