If it runs down to your foot, it is probably sciatica, if it goes only as far as the knee it may be Piriformis Syndrome. (false sciatica) The piriformis is the deepest of the 4 glute (butt) muscles, and is prone to contracting, causing pain. It is a huge muscle compared to most of the muscles in the body, and can cause pain from the neck to the knees if it is contracting. It can often be worked out with massage, or as someone else posted, stretches or yoga. If you have someone that you are close enough to have them do this, have them take the heel of their hand and compress the butt from the sacrum, (the big bone at the base of your spine) out to the hip joint. Not too hard, but hard enough for you to feel pressure. Do the same compressions all over the whole butt area. If you can get that muscle loosened, even a little, it can give you some releif. Good old fashioned Epsom Salt soaks can be helpful, too. Feel Better!