I have begun to have pain in the buttocks with prolonged sitting, started about six weeks back, i don't have back pain, there is no numbness in the legs and the pain does not radiate to the legs.

Pelvic source pain: In an otherwise healthy 50 yo, the most common cause is a spasm in ,the piriformis muscle, which lies over the sciatic nerve. It can be irritated with a wallet on the same side, sacral sitting ( sliding buttock forward when seated) or direct trauma. Another common cause is sacro iliac irritation. Chiropractic, or PMR docs can evaluate this. X rays or MRI won't show it.