Sounds like this is getting expensive. Find a vet you trust, holistic maybe, and stick with him/her. If the vet's not sure whats wrong, you could spend a lot of time looking around getting different opinions.
If the vet gives you advice that YOU think makes sense, go with it. A lot of vets have their own little circle of experts that they deal with, such as a chiropractor, pharmacist etc.
Good Luck.
