Hello, I Have Been A Runner For 35 Years. For

Hello, I have been a runner for 35 years. For the last 5 years, I have experienced pain in the middle of my left buttocks after running. The pain is chronic and doesn't readily go away. Many nights, I can't sleep because of the discomfort. Sometimes the pain travels under my ilium, down the inside of my left thigh and circles around my calf just below my knee, to the point that I can't put weight on my left leg. A physical therapist thought the piriformis muscle might be pinching the sciatic nerve, but as I look at the 3D diagram of the sciatic nerve, the nerve goes to the outside of the thigh, not the inside of the thigh. Any thoughts on what could be causing the pain?