It does look irritated, but it doesn't look like anything too major. I would probably clean it with some betadine solution (you could just dilute the betadine until it is tea colored and soak him if you want). As for why it hasn't gone away yet, snakes heal differently than we do. We shed skin cells all the time, and they shed their entire skin all at once. So you likely won't see an improvement until his next shed.