have you tried benadryl?
i had a TERRIBLE breakout (the worst in my life) after a reaction to an iron infusion. i literally could not function enough to eat, sleep, do anything. i was scratching day and night and putting ice packs all over myself. basically, during those horrendous two weeks, i took benadryl every day to try and sleep the time away because being awake was pure hell.
you could also try doxepin but you'd need a prescription. it's basically a SUPER strong benadryl.