Hello and welcome to Just Answer. I am a licensed veterinarian and would be happy to answer your questions.
If you have already tried all of the above mentioned treatments from your vet, it is most likely that they have ruled out a bacterial or yeast infection of that area. They can occur even without the presence of lesions and can contribute to the itch. They are easily identified with a test called a skin cytology that evaluates the cells on the surface of the skin and looks for overgrowth of these organisms. If present, they need to be treated as a separate issue.
What it sounds like Oprah is dealing with is a condition called atopic dermatitis. Atopic dermatitis (AD) or eczema is a long-lasting (chronic) condition that causes itchy inflammation of the skin and ears. It may affect any area, but it is usually affects the face, feet, armpits, trunk, and abdomen. It may be persistent or it may flare periodically and then subside. These can make a dog's skin itch and there may or may not be other skin lesions visible. Itching problems in pets can be difficult to diagnose and the history and response to medications tried are a very important part of figuring out the cause
Animals with AD have two main problems. The first is an abnormal skin surface (barrier) which leads to sensitive skin. The second is an overactive immune system that reacts to a variety of flare factors. Recognized flare factors include: dry skin, food allergens, parasites (fleas), infection (bacterial or yeast), and environmental allergens, like dust, pollen, molds, etc . When a flare occurs, your pet will itch more and may develop red, flaky, and/or infected skin or ears, as these areas are then invaded by bacteria or yeast.
Since AD symptoms can be a seasonal or year round problem, treating them or the secondary infections at any given time, does not mean the signs are gone for good and the symptoms may recur throughout the year. Although there is no cure for AD, it's symptoms can be treated with a variety of therapies/medications. If recurrences are frequent, the focus must shift to identifying the specific triggers of the allergic reactions with things like skin testing or food trials and then practicing avoidance as best possible.
Treatment for all animals with AD should include:
1) Dermoscent® - helps to restore the lipid layer of the skin and helps to maintain it's hydration and normal skin defenses against allergens, especially the barrier function. See link: Dermoscent.
2) Allerderm Spot On® - help repair and restore the epidermal (skin) barrier in canine and feline patients suffering from skin disease. See link: Allerderm spot on
3) Sogeval® DOUXO® Seborrhea Spot-on - helps to restructure the epidermal barrier and control inflammation. See link: Douxo Spot on
If you haven't tried any of these barrier type products yet, it would make sense to give them a try. There is not any one product that will help, but these newer products, in combination with some of the other things you have tried may help.
Good luck and please let me know if you have any further questions.