Suggest Treatment For Pain In Ankle After A Fracture

Hi, I fractured my ankle recently, about a week ago, got a cast about 3 days ago, every time I have my foot in a vertical hanging position, i get a really really sharp pain where my ankle is, it isnt there when im lying down or have the leg resting on something horizontal, but when its vertical the pain is so bad, is this something to do with the cast, or....?