I use crutches after injured ankle, and foot becomes very red and purple and my foot begins to throb?

Last week I injured my left ankle from a heavy wood pallet fell off a stack of pallets and hit me on my left ankle. After the blow my ankle became very swollen and bruised. After the injury I was taken to the ER where the Dr did an X-ray of my ankle and said my ankle had a very bad Sprain. Well 9 days later my ankle is still bruised and swollen but my main concern is I am on crutches and everytime I use my crutches my injured ankle and foot becomes very red and purple and my foot begins to throb. My question i guess is is this normal for my ankle and foot to turn colors like this and does this sound like a broken ankle or a sprained ankle?