It could be a disc problem. However, veterinary chiropractic or acupuncture can help decrease the pressure on the nerves and let the area heal. Your veterinarian may prescribe steroids and muscle relaxers in the meantime. It is important to restrict movement to prevent further injury. You need to get started on treatment now. I would try Promaxol to reduce the pain and help healing to begin. Promaxol would be a good choice for your dog because it contains the stronger LM potencies.
After improvement is seen then you can switch over to Arthro-IonX. In addition it is helpful to give digestive enzymes with each meal, MSM, probiotics, and fish oil. The oligotherapeutic mineral base found in the IONX products helps the body to better utilize the other nutritional substances given for a synergistic response and faster healing.
Also be sure to give sufficient fresh water that is free of chlorine and fluoride. If you can gradually phase into a grain free diet that can be helpful too.
Please let us know how you progress or if you have any other questions.