What Causes Persistent Pain In The Right Leg?

I had a sudden onset of right leg pain last night, it was not brought on by any exercise or injury. . It was excruciating, like a charleyhorse, but with pain all the way down my leg, and numbness in my ankle and foot. Today the pain continues, centered at the back of my knee and going down the calf . It is worse with walking. I can t bear weight or bend my knee. I don t see any redness or swelling in my leg and it is not tender to touch. I can do straight leg raises with no increased pain. I ve been using a heating pad with my leg elevated. I ve taken naproxen and gabapentin with no relief.