You can consult a pediatrician
for ruling out the cause of persistent vomiting
if not yet consulted and also you have not mentioned regarding any investigation if done uptil now.
probable causes of persistent vomiting since hepatitis
/any irritable bowel disease /some higher centre disorder or simply some sort of intolerance of food for some specific food item,but it needs to be ruled out throughly for safety.
temporaraily you can give Ipecac 200 one dose once in day for stopping vomiting and vomiting sensation
Please update your son's status after through investation.