He would require an anti emetic based on his weight to control the vomiting. I would advise you to meet a pediatrician so that he can be examined and undergo the necessary investigations to find the underlying cause of the problem and have it treated accordingly. Kindly ensure that he stays well hydrated and give him ORS supplementation.

Rule out onset of jaundice,as loss of appetite and nausea and vomiting are initial symptoms of hepatitis. Plz consult your paediatrician for physical examination and treatment. Till then,use syp ondem for vomiting half hour before meals.