
Hi Elliejake,
I feel for you, the minute I saw this thread I knew it was going to be a bit of a quagmire of opinion! (Allergies and 'allergies' causes the same in even in the medical/veterinary worlds too,so no surprises that feeds down to the populous!)
Your Vet has already embarked on some exploratory work, so obviously is best placed having been hands and eyes on the dog (unlike Internet users on a keyboard) to be honest there is a potential allergen for every member of this forum (could be a long thread if they did all pitch a suggestion!)
Then there is the 'skin condition' spectrum still to run through....!
I would say your best bet is to persevere (and pester if necessary) your Vet to assist you. Without proper testing and hands, nose and eyes on the animal every other potential diagnosis is moot!
When I had this same problem with one of my dogs, what I found useful was to keep a diary, of where my dog had been and what she had eaten.. A whole day in the life of! This really helped to brain storm with my Vet as to realistic possibilities.
I would also suggest that meantime, alleviating your dogs symptoms ( until you can cure the symptoms) would be a kindness and relief! And lessen your stress for your dogs comfort first and foremost and showring performance there after.
Neem oil has already been suggested ( I have also used this with good results)
With a dog I had ( a Eurasier) I eventually found the cause to be a particular bush in our field that she liked to ratch about in and lie under ~ I used
Quistel~Bio restoring lotion and shampoo the lotion is a liquid spray that you can spritz onto the affected area ( and its fine if the dog does then lick that area... Unlike Thornit which has been recommended) within a day of using Quistel I had dramatic positive effects and no worrying of the area by my dog.
I like Nova's suggestion of using an anti-histamine to see if symptoms reduce and point to allergy.. However I would do this after discussion with your vet as to which would be the best anti-histamine to give your dog and as your vet knows your dogs history, wether this treatment and what dosage will be ok for your dog.
Sympathise with you as I've been there.