In the last twelve years, I have had three instances with three different dogs (and three different vets) that were given COMPLETELY wrong diagnoses:

Greyhound (Rocket) hunching - vet diagnosed a bowel obstruction...and did MANY expensive treatments and tests. No improvement. New vet found that he had a disk in his neck that was inflamed. Rimadyl for a while and he was a new dog.

Great Dane (Baby) severe peeing problems - vet diagnosed kidney failure. My precious Baby even had a 'put to sleep' date scheduled. I really liked this vet and felt like I was betraying him by seeing a new vet...but Baby was the most important thing. The new vet found a very mild bladder infection. Baby lived another two and a half years.

Mini Dachshund (Linus) lethargic, not eating, severe vomiting - vet diagnosed pancreatitis and treated it for two weeks. They didnt pursue any other possible causes. My little guy was SICK but his blood work was getting better. The vet humored us, but I could tell they felt we were being 'overprotective parents'. I drove from Omaha to the vet hospital in Manhattan KS. Linus had a piece of toy lodged in his small intestine. Emergency surgery and two weeks of touch and go (a second surgery due to leakage) I couldnt leave him and spent two weeks in a hotel so that I could visit him twice a day. Today Linus is doing GREAT!

Please visit my pet tribute website and you can read a thorough account of Baby's last couple of years. There is also a heartbreaking account of Rocket's last week. I cry every time I think about him...and it has been four years now.
http://www.griefonline.com

PLEASE get a second opinion if your pet is not getting better!