My five year old boy has the same thing and it is accompanied by frequent ear infections
we have spent two years changing his diet, doing elimination diets, trying OTC allergy meds, lots of vet visits etc.
In addition to the hives, he also has a skin condition called sebaceous adenitis, which causes his hair to fall out (yeah he's a total mess).
We have finally decided to switch him to a raw diet, because we believe (the vet, the dermatologist and us) that the ear infections and what appear to be hives are being caused by both an allergy to something that is not food related an possibly yeast issues (which are being fuelled by the dry dog food)
Our vet does not want to put him on a steroid or other prescription medication before we have exhausted all other possible solutions.
so besides the raw diet, he also gets an Omega 6 oil supplement, a Vitamin E, and Vitamin A supplement everyday and once a week he gets a shower using Vetoquinol Care shampoo, which is a medicated shampoo that is antibacterial and anti fungal and helps with removing any crusts or scales that form.
The shampoo has helped a lot with the skin problems as has the switch to the raw diet. The picture above was taken about five minutes ago. he is due a shampoo, the bumps pretty much disappear after the shampoo for a few days.