Have you ever considered consulting with a vet trained in either a homeopathy or traditional chinese medicine ?
I ask because one of my dogs has suffered from a whole variety of issues, digestive and otherwise, which regular vets could never figure out and treated as distinct, unrelated issues, though I always suspected that they were interconnected. This resulted in years of frustration and little to no progress.
I found much more helpful information with holistic medicinal practices which acknowledged and understood both things that I observed but could not be accounted for using blood tests, xrays, etc. and for the relationships between "unconnected" issues. It also offered alternatives to drugs which, in my case at least, offered at best very short term results and had negative long term effects on a dog who's whole body was just profoundly out of whack.
You can search for a vet with training in TCM here
and homeopathic vets here
, though in both cases I would call and ask about the particular vet's training, certification and experience before making an appointment (many do phone consults). As with anything, there are those with very little training/experience who advertise themselves as "holistic vets", but really will have little to offer you.
A couple of books that I've found extremely helpful are Homeopathic Care for Cats and Dogs: Small Doses for Small Animals
and Four Paws Five Directions : A Guide to Chinese Medicine for Cats and Dogs