Hi Ted.
My Polli, an almost 9 year old brood mama started limping in late Sept. - 1 week later, no improvement so I brought her in to the vet. She was calm enough that the vet said they could do some xrays of the leg/foot. Nothing showed up, not even arthritis. We had stopped all walks, let her out back on leash only, picked her up each and every time she wanted on our bed, etc. (OH MY back!)
One week later there was no improvement. I took her back in and this time it had to be under anethesia for a complete set of xrays, neck, shoulder, spine etc. She was npot limping the morning I brought her in, but we brouth her in anyway.
The x-rays showed nothing again. BUT... she was basically crippled from all the manipulation they had to do in order to get the pictures. It was so sad, she looked like IGOR from Young Frankenstein. We continued no walks, picking her up,deramaxx for pain, tramedol when indicated (for us, it was when she was panting out of the blue which did not happen very often).
The x-rays were sent to Cornell Univsersity and OSU, they all said the same thing. Nothing. It was good, but frustrating> we knew the next step was an MRI to determine if it were a disk.
I wanted to hold off and my vet suggested I do as well.
5 weeks later (now) Polli is virtully limp free. Her gait will be a little bit off when she is on concrete/ pavemenet so I limit he to grass only.
As long as your pup is comfortable, give it some time. In the meantime, see if you can find a vet who practices holistically, acupuncture etc. Speak to them via phone and discuss it so that if you need to bring him in, you don;t need to do your research when you need someone right away.
I know how frustrating and helpless you feel when you don't know what it is or how to fix it.
My thoughts are with you. Keep us informed.