Hello, and thanks for writing in. It sounds suspicious that Carl may be dealing with allergies, which are common this time of year. Allergies in dogs common manifest themselves with skin problems (mainly being itchy, or licking at the paws). Having an itchy butt can go right along with it, especially if the anal glands are not full, and you are not seeing any fleas. There are many ways to go about treated allergy symptoms in dogs, such as many of the things you mentioned (cortisone, fatty acids (fish oil), antihistamines, low-allergen foods, etc.) Yes, cortisone and antihistamines are reasonable ways to treat the symptoms. Cortisone can be given as injections or pills, and may need to be repeated periodically, depending on the severity of symptoms. You can give over the counter Benadryl (diphenhydramine) at 1mg per pound of body weight, every 8-12 hours. It may cause drowsiness, but is quite safe. You can even do both Benadryl and cortisone at the same time. Cortisone is likely the most effective, but can have side effects. Short-term side effects include increased thirst and urination, and increased appetite. If a dog is given many cortisone injections, or is on long-term cortisone pills, you may run into other problems, such as liver or adrenal gland problems down the road. You may want to consider a low-allergen food, such as Purina HA, Purina DRM, Hill's Z/D, Hill's D/D, or Iams FP foods. They can help with many allergy problems, even if a food allergy is not the issue. You would need to get these foods through a veterinarian.
Anti-itch shampoos can be used to help temporarily. There are good ones you can get from a veterinarian, including oatmeal-based shampoos. Lastly, you can ask your veterinarian about a medicine called Atopica. It can help in most dogs to control allergy symptoms, instead of using cortisone. It's quite potent, but it's not cheap. It's a nice alternative to cortisone, especially if there is any concern about the possible long-term side effects of cortisone. I hope this helps. Dr. Dave