Hi, Welcome to JustAnswer. I am a licensed veterinarian and I'd like to assist you and Barney. Itchy bumpy skin could be due to several causes: an hormonal imbalance, a bacterial skin infection, a yeast skin infection, allergies, or mange. The treatment would definitely depend upon the cause. Barney needs to have your vet there diagnose the cause, so that he could be specifically treated.
Until you can get him to a vet, you could give him some benadryl which would likely help with allergies and would be safe. The dose is 1mg/pound (or 2.2 mg/ kg) every 8 hours.