Has he been sick lately? Has he eaten anything different lately? I ask because there is different types of hives.
Some that are raised and thick are often thought to be contact. They aren't always and it matters. I would call the allergist AGAIN. They can at least rule out allergies before he has a reaction.
Why is he coughing? Is he sick or has he been sick? My close friend is an allergist, she tells me that there are MULTIPLE symptoms for allergies, and there is a type of hive you can have at the end of a virus.
Did you change ANY detergent, etc.? Have you taken him to the dry cleaner?
You can take him to the ER and they will give him an epi shot and will check his ears and the rash. Take a picture of the rash!!! Sometimes when it is a food allergy, the ears itching can be the beginning warning to anaphalactic (sp) shock.
I have contact allergies...I don't handle anything with formaldehyde well. Which rules out just about ALL cleansers.