White blister-like spot (White's tree frog)

[CatEyeLeachie]

My WTF got this odd white spot over his ear. He is active, has good appetite and don't react when I touch it.
Have any of you guys seen something like this before? I'm taking him to the vet if it gets worse or don't start healing soon.

This is the third time he's got health problems, and he is not that old. None of my other frogs or reptiles get sick, so I'm starting to wonder if there's something wrong with him or if he just has bad luck