[cypher]

You're probably cleaning your cage more frequently than most of us so I doubt very much that the amount of cage cleaning has anything to do with Charlie's condition.
It's very hard to say what it might be tbh, it's not a particularly common area to see a problem with mites for example but that could be a possibility.
What substrate do you use, any changes there?
I know getting to a vet can be difficult in the current situation but most vets have made arrangements to make it possible for them to continue to see sick animals so I would phone around the vets in your area & ask about taking him in, as the condition is getting worse I really do think it's important to get him seen if you possibly can.