The vet just left. He didn't really have an answer for me. He watched Jack walk and trot and also performed a flexion test on him and he passed with flying colors. He said that there were no signs of arthritis that he could tell, his back was not sore, and took some blood to test for lyme. He thought that Jack looked completely healthy, complimented me on my trim job, and recommended to start using a grazing muzzle as Jack was borderline fat.lol. He suggested that I give him bute before really strenuous exercise and work him alot on walking and trotting (big circles are ok) to get him really strong before I start working on his canter again. I can't wait for the results of the Lyme test to come back! Something tells me he has it... we'll see though!