Hello and welcome to healthcaremagic
I would keep a possibility of Acute
Urticaria. It presents as itching and skin welts/swellings, which can be distributed all over the body.
Urticaria OR hives can occur due to various causes like(to name a few):
--Infections(bacterial , viral, fungal)
--Drugs(Pain killers/ antibiotics etc)
--Certain foods and food additives/preservatives
--Physical Urticaria: Cold temperature, Heat, Pressure(Prolonged Standing, Sitting), Dermaographism etc.
--Cholinergic Urticaria: in response to strong emotions, exercise, spicy food etc --
Autoimmune disorders like SLE, RA etc.
--A few cases have no underlying cause and are known as idiopathic urticaria.
An oral antihistamine like
Fexofenadine (Allegra 90 mg tab) OR
Loratadine (Alaspan 10mg tablet) once or twice daily for a week would be suitable. They are non-sedating and wont affect his alertness level.
A topical soothing lotion like
calamine would help him symptomatically.
take care
regards