Thanks for your quick replies!
His ears were already starting to be tattered before he took the medicine he's taking now.
The vet that saw him did take a sample from his ears but said it's not a big deal and not bothering him so he didn't give any immediate treatment.
I might go to another vet for a second opinion.
I've been trying to check on a dark cloth if there are any mites or anything but I can't see anything moving.
So, I'll give the cage/wheel another good clean and see if I can get any help.
He just seems to suddenly have a lot of problems come up at once. He's 3 years old, by the way. And never had any health issues before now.