I was stung on the side of my leg between my knee and ankle yesterday and today my foot is so swollen that I can't wear shoes. Is this normal?

Can be. The sting was above the ankle - the body shifts fluids to the area in response to the venom to help your body heal. Gravity pulls the fluid down into the lower leg/foot. Your swelling sounds pretty profound. Consider getting an MD to check it out - especially if issues like diabetes. http://www.webmd.com/skin-problems-and-treatments/insect-stings.