I was diagnosed with arthritis in my left buttock and now I have bands of pain just below my buttocks. Sometimes these bands of pain are about halfway down my leg.
Arthritis is a joint condition, not a muscle condition, so there is some misunderstanding here. Perhaps arthritis of the hip or sacro-iliac joint. Both can cause pain in the upper leg.
The sciatic nerve emerges from the pelvis through a large foramen, and passes down the back of the leg. Sitting in an upright chair, straight first one leg, and then the other parallel to the ground. Inordinately painful in the back of the leg or buttock? Does forward bending, or backward for that matter, provoke the pain?
All of these would point to a joint condition in the pelvis or lower back, routinely treated by chiropractors, that could be causing your symptoms.
I'd talk to friends and your doctor and get the name of an experienced chiropractor in your town. Take your X-rays with you.
Try doing some lower back exercises routinely every morning before getting out of bed. Type "back exercises" into the Search this site at Chiropractic-Help.
I hope this contributes.
Dr. Barrie Lewis