R.K.
My Mom, myself, my son and granddaughter have all suffered with hives. The only thing that ever worked was Benedryl. Give them a dose, get them comfortable on the couch or in bed put in a movie and they will sleep. It's better to keep them a little cool than a little warm. For some reason being too warm makes the itching worse.
The biggest thing to worry about is -- if they start in his throat that is also known as anaphylactic shock, the throat can close up and hinder or stop breathing.
Please I am not trying to scare you, but this was something I never knew and wish I had.
Relax, give him Benedryl, let him sleep but watch his breathing. It can take a week or more for them to go away.