my son he is in 4 and half years. his problem is vomiting while eating any food and consipation. he is also underweight what can i do

A. Viral gastroenteritis, commonly called 'gastro', is one of the most common reasons for acute vomiting in children, although other types of infections such as a cold or urinary tract infection can also cause vomiting. Food poisoning or food allergy can also cause vomiting.