Thanks for your query. By what you describe it is more likely to be urticaria
. However it is better that you consult a doctor who will be the best person to guide you.
Urticaria is a manifestaion of an allergic reaction
to food or medicine. Anti-histamine
should help and since it has not worked in your son's case it is all the more to know the exact problem.
Wishing your son an early recovery.