Sciatica is merely a set of symptoms, not a condition in and of itself. Assuming you're not pregnant, the irritation and flaring of the sciatic nerve can be attributed to any number of other causes, the next most common of which are spinal disc herniation or trauma to the lower spine such as from a sports injury or car accident. Outhouse is right though. Get thee to a doctor. The longer you wait, the more it's going to hurt.