I have a 3 year old son. From the time he was about 1.5 years old he would experience bouts of chronic diarrhea that would last for 1-2 weeks. He had no other symptoms. We went to the pediatrician and he recommended a lactose-free diet. Fast-forward to present time. My son has light colored stools (clay/light tan), frequent loose stools, and stomach aches on an almost daily basis. His growth/weight are on track and consistent. What tests should I request to find out what is wrong with him?