could be some sort of allergic reaction. are there similarities in the foods he can/can't keep down?
what causes nausea and vomiting after eating in a teenage male. my son is 17 and has had this issue before he was given nexium. he was not able to take that medicine and it was changed to something similar. it did help and he was on it for about a month. he didn't need it for a while and now the nausea and occasional vomiting after eating has started again.