I have a question for the runners or PT's: on longer runs, Ive been getting an irritation on the tops of the back of my thighs... (think, sort of on the inside of the sits bones), which travels down the back of my legs a bit. Basically, my butt hurts!

Ive been training for a marathon, we just completed the 18 miler today.

Any idea what this is, and any stretches to combat the irritation?

Thanks--

Jen