I think you should try to find a veterinary chiropractor. It usually makes a big difference for my patients that have similar symptoms. I also use Arthro-IonX. It helps to decrease pain and inflammation and stimulate healing. In addition I find it helpful to follow a holistic approach by giving some nutritional supplements to accompany Arthro-IonX. The supplements I recommend are digestive enzymes with meals, MSM, probiotics, and fish oil. Arthro-IonX will help the body to better utilize the nutrition for a synergistic response. While the rear end is weak try to help him get up and steady him while walking so that he doesn't fall over and hurt himself. You can do this with a towel folded lengthwise and placed under his tummy. You lift up on the two ends and walk with him so that he doesn't have to bear all his weight.
Please let us know how you do or if you have any other questions.