My son has been coming out in hives as well. Although we think his allergy is to hairy caterpilla's (or itchy grubs) his was quite severe though and needed a trip to the hospital. He was on Phenergan but ended up needing redipred (prednisone) to settle it down.

As for relief we tried dermaid (over the counter cream) it helped the first 2 times but the 3rd time it stung

If you go to your local pharmacy they will direct you to what is the nest relief cream to use