Depends. If it's centered around your hip and radiating down your leg or up into your lower back, it could be sciatica.
If it's below the knee & on the inside, it could be Medial Tibial Stress Syndrome, or shin splints...
...Either that, or you need to stop carrying your keys in your back pocket.
English
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Pretty sure it's sciatica, thanks
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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.