My Dogs itching/allergy problem plz help

I think my pomeranian has some immune problems of some sort....has had itching and coughing problems for years.Bites herself raw alot and recently constantly scratching and biting with skin flaky,crusty and red inflamed all over.I tried Antibiotics and Temaril for a month which seemed\ to work good but she ran out and it all came back with a vengeance....Is there any natural remedies that work to supercharge her immune system and knock out the allergy/skin problem and the biting?Im looking for heavy guns here because she is really out of whack...much thx for all input
J