greetings. Its great if you have already taken him to a specialist. Conditions a such need a more keen and critical evaluation. Will like to know exactly at what times of the day the child vomits more, or the complains of any headaches
when he gets up or visual blurring. This could be suggestive of intracranial hypertension
, which off course should be a rare outcome in this child.
Before concluding that this could be a psychological problem, I think its worth seeing this child being consulted by a pediatric surgeon or gastroenereologist. It shall very interesting doing endoscopic exams to exclude any upper gastroinetstinal obstruction or late clinically apparent malformations. Seeing a gastroenteroogist and a pediatric surgeon to get expert advise is my opinion. If all is fine, then we can really think its psychological.
Wishing you the best and quick health regain for the child,