the root of your problem might be located in your lower back. i have had similar pain before, and i was told by my chiropractor that i have a sciatic nerve that is pinched every once in awhile, resulting in a similar kind of pain to yours. i don't remember exactly how the muscles in the back are attached to those in your legs, but try to make an effort to stretch your lower back out as well as your legs, and see if that helps.
hope you feel better.
-christopher
"It's better to be dead and cool....than alive and uncool." - Mickey Rourke in "Harley Davidson and the Marlboro Man"