Your pup is probably experiencing Intervetebral disc disease which is when there is a substance build up in the disc that presses against the spine. YOur vet should be able to see something with radio graphs.
Symptoms are just what you are describing. Sometimes medication is all that is required sometimes surgery is required depending on the severity. Since the do is feeling better when you arrive home it may be because he is able to rest comfortably thereby bringing the swelling down.
You can read more on this here:
If this is in the lower spine it may be hip dysplasia. For pain , you can give aspirin, 1 children's aspirin for every 16 lbs of body weight, or 1 adult aspirin for every 32 lbs of body weight. Make sure it is aspirin and not Tylenol, Advil or anything with acetaminophen. However this should not be long term use or other problems with the stomach may appear. Try calling the vet and explain the pain, they may be able to give her rimadyl.
Also add some glucosamine to her diet to help with the build up of cartilage.
I am sorry that you are not satisfied with the answer. I will direct your queston to another expert .
I am not sure what advice you are seeking aside from keeping the dog comfortable and out of pain.