I do not know if this is the case or not but he might have a chronic infection in his hip area. I know it happened to one of my dogs. There was nothing you could see or smell but he got into a fight with one of my other dogs and I guess he got a small cut I did not see and the infection started then. He was limping and when I would push on his hip he would yelp a little. I mixed fresh mashed garlic and mixed it with some butter (he would not eat it in his food) and put it down his throat right before his meal. I also mixed some cayenne (not the super hot kind) in water and with a syringe squirt just a little in his mouth and later like 1/2 tsp. I made sure it did not get splashed anywhere else but he really did not act as he minded the hot stuff. I did the cayenne only two or three times and with the garlic I saw major improvement. For building collagen, I mixed DE (diatemous earth) in his water. I did not mix DE with his food, I mixed it in his water so every time he would drink he would get some silica.
It does not hurt to try the garlic. But try to only give like 1 - 2 cloves a day not more than that, and for only 4 or 5 days. Garlic like onion can cause some problems.