I'm a 15 yr old female XC runner and 2 weeks ago after running hills I had bad tightness and pain in my left buttock. I rested for a week, saw an ortho who said it was probably a small muscle strain. However, it is definitely not muscle pain. My sit bone feels tight and aches when sitting for long periods of time. I returned to practice and am doing very light mileage, only 4 miles today. It doesn't hurt while running, but I do get a tightness in the area. I can walk and hop on it without pain and it feels better when standing. When I sit I get a bad achy pain and the bone is tender to the touch. What could this be?