I'm sorry to hear about your Yorkie's ordeal, Rob. Besides seeing another doc, or perhaps a specialist in this kind of area, I don't know what else to suggest.
Here's some stuff on Addison's Disease:
Some of the most common signs a pet owner may observe in a dog with Canine Addison's Disease include:
Anorexia
Lack of energy
Weakness
Vomiting
Diarrhea
Weight loss
Dehydration
Less frequent signs include:
Bloody vomit or stool
Excessive thirst or urination
Loss of appetite
Hair loss
Shaking and tremors
Most veterinarians will treat Canine Addison's Disease with a medication that replaces the hormones that the adrenal glands can no longer produce. Today, the only medication approved by the FDA* for treating Canine Addison's Disease is PERCORTEN®-V (desoxycorticosterone pivalate).
http://www.petwellness.com/daddisons.asp