Did the Vet ever determine what was the cause of the pain? Was it a disc in the back that was ruptured? Does your dog have feeling in it's back legs? You can determine this by pinching your dog's toes and if he pulls away that is a good sign. It sounds to me as if your pet had some type of back injury. There are several medications which your Vet can try to help with this problem. These are some of the medications we would use on a dog at our practice with back pain/disc problems. Methocarbamol (robaxin) this medication is a muscle relaxor. It helps pets that are having muscle spasms from the pinched nerves in the back. We also place these patients on prednisone or a non-steroidal anti-inflammatory medication depending on the patient's severity. We have placed some patients with degenterive disc disease on a medication called gabapentin. This particular medication is a human med that was originally designed for eplileptic patients. This medication was also found to be beneficial for patients with burning, neuropathic,and lancinating pain the dose is 1-10mg/kg by mouth daily. You are welcome to share this information with your Vet. I took the information for gabapentin out of Kirk and Bistner's Veterinary Procedures and Emergency treatment. I hope this helps and I wish you the best of luck, Andrea