He might be having infection of the gastrointestinal tract...A stool examination will help in confirming the diagnosis.... Advice him to Drink plenty of fluids,coconut water,avoid Pulses and Beans, food with high amounts of refined sugars will help...I would advice himto take pantoprazole 40 mg once a day before meals along with Domperidone 30 mg and a probiotic...further treatment depends upon stool examination and clinical assessment of dehydration...Consult nearest physician they will do the needful.