From your description of skin problems, I think you are dealing with an allergy condition and your dog has developed an ear infection.
You can read up on allergies here:
A lot of dogs have an allergic reaction to corn and wheat and other items in dog foods, so you may want to switch dog foods to one that does not contain corn or wheat or try the elimination method I mention at the end of my answer. It may take several weeks to see improvement after the change of food. You may also give your dog Benadryl up to 2mg per pound every 8 hours.
There might be a secondary skin condition in addition to the allergy such as staph dermatitis or yeast dermatitis. Staph usually occurs on the lower regions of your pet and tends to have small pimple type bumps. Shampoo containing Chlorhexiderm and/or Oatmeal can help with this condition though it does not cure the allergy. Yeast typically shows as a greasy area that has a sweet musty odor. Sometimes the skin can become inflamed, darker and thickened due to itching. Yeast likes areas such as between toes, armpits and ears. Selsun Blue Shampoo can help with Yeast dermatitis. When shampooing, lather and leave on 15 minutes before rinsing. These shampoos are not meant to be a cure, just a relief.
It sounds like your dog has developed an ear infection. It is probably a yeast or bacterial infection. You can use a mixture of distilled vinegar, water and alcohol on a cotton ball to gently clean the ear.
In a yeast infection, you will see black buildup in the ear. You may also notice redness and bleeding, head shaking and your dog scratching the ear as well. You can try some miconazole cream to see if it helps until you can get in to see the Vet, but it isn’t a cure for underlying condition
You will have to have your vet look at it and determine if it is fungal or bacterial in nature so the appropriate medication can be given. Ear infections are not pleasant for your dog and I hope you can get him seen soon.
The following site has a recipe for a home remedy that may provide some relief though I recommend visiting the vet for medication.
Allergies are very frustrating to deal with as you can treat the symptoms, but as long as the allergen isn't identified, it keeps coming back. You may want to see a dermatologist to determine the exact cause for the allergy or use the elimination method described on the following website. http://allergies.about.com/cs/canine/a/aa091800a.htm
Hope this helps.