i had this happen to me before when i was in my 20's. i had a bad cold..terrible cough.. it was october.. nothing out of the ordinary but as i recovered from the virus i developed hives EVERYWHERE on my body. i had to miss work. i think i put baking soda paste over them to relieve them, i remember that feeling good. dr told me it was from the virus i had. it was maybe 10 years ago so i cant remember details .. it seemed to last forever .. i remeber it didnt instantly just go away but gradually got better.. i also took benadryl but the baking soda paste really helped. it only happened to me that once in my entire life.... so strange but i guess that is what is was . hope your son feels better soon!