Hello, I'm Dr. Deb and will do my best to help you today.
I recently came online and see that your question about Barnabas hasn't been answered. I'm so sorry that you've had to wait for a response, but if you still need assistance, I'd like to help if I can.
It sounds as if he may have a condition called Panosteitis based on your description of his behavior. This condition is essentially inflammation in the long bones of young, mostly large breed dogs. (http://www.petmd.com/dog/conditions/musculoskeletal/c_multi_panosteitis)
It's a shame that the vets can't or don't take x-rays where you live since this condition is easily diagnosed based on characteristic changes in the bone marrow.
This condition is also known as growing pains since most dogs will outgrow it with no long lasting consequences or issues.
Treatment is primarily controlling the pain associated with it. I typically dispense non-steroidal anti-inflammatory drugs such as Rimadyl, Deramaxx, Previcoxx or Meloxicam although I'm not certain what drugs you have available there. I'll also dispense a specific anti-pain drug such as Tramadol or Gabapentin.
Some of the patients I've seen will only experience one episode while others will appear to improve but have relapses again in a few weeks or months. But, they will all outgrow the problem eventually...at least that's been my experience.
I hope this helps although, again, my profuse apologies for the delayed reply. Deb