I will assume he feeds himself , so put healthy amounts of food in front of him, let him eat himself, if he yells for more and you know he has had enough , distract him with a game ,read a book, do the jig, music soothes the savage breast, As the pediatrician has said he is okay ,if he is constipated there are childrens probiotics now to help with this there is powdered probiotics you can sprinkle on their food and also child yoghourts.