Ah, you have my sympathies! Broke my foot two weeks ago and, like you, I walked about on it for a week before I realised it was broken.
I got a cast cover called a LimbO off the Internet for showering. Really good as it has a good rubber seal at the top. Also read on the Net that if it gets really itchy inside, a blast down it with the hairdryer on a cool setting is good. Haven't tried it yet myself.