i had similar problem last month. very strange. it turned out i got a pinched nerve or two or three somewhere in lower back and hips region. i told my chiropractor and he did his usual snap-crackle-n-pop to my lower back and the problem went away. but the pain now moves up to my ass, which i think is caused by a pinch nerve in my brain which made me saying things, that would activate "boot kicking up ass" respond from other folks.