HELP Pls..my son with digestive problem

My son 6 years 2 months have a big problem with his digestive. His belly is always bloating, gas, reflux, all day long. Even drinks water, the waters will sits on his stomach. I have running SCD diets with very little kinds of foods but he is still very thin with very big belly. Seems he can not absorb nutition from food and supplementions. Somebody pls tell how to do to heal his digestive problem. Thank you..