I certainly would do something. Because of a wrong diagnosis your poor dog has been suffering unnecessarily, and what makes is so much worse is that the wrong diagnosis made was of something that a vet should have found easy to see.

You are in the UK right? If so this may help in deciding what to do next.

http://www.provet.co.uk/petfacts/dis...terinarian.htm

Good luck and please let us know how your dog is doing now.