11 year old boy awoke with hives from unknown cause 2 nights in a row. the next two nights no hives but vomited one each night. is this part of hives?

Hard to say, but: Without a good examination, it is difficult to know what is going on for this youngster, but hives can be quite dangerous and i recommend making an appointment for him to visit to a doctor and until then, even an urgent care or er if the hives recur during a night. The antihistamine is a good idea until he is seen. You might want to ask the doctor for an epi-pin rx for an emergency. Best!

Viral infection: I think these are likely some of the manifestation of a viral infection which started with hives then other symptoms. If the vomiting fails to resolve in a couple more days, then you need to bring him to a doctor. In the meanwhile , be sure to keep him hydrated. He would not starve if he only eats a little