I never heard of cats having yeast in the ears. What does it look like? How do they get it?
Cats also get a yeast in their ears that causes shaking of the head, then excessive shaking can cause the hematomas to either start or get worse if already there.
If no sign of mites have the vet swab and check for yeast.
let us know how it turns out.
Your cat might have ear mites. Look in your cats' ears, if you see black dots or black junk in his ears, then that's what it is. You can buy ear mite med in any store, no need to see the vet for this. If there's no black stuff in the ears, then I'd take the cat to the vet.
I've noticed that cats that suffer ear hematoma will do this whenever the ear is touched (by kitty or others). At your next vet visit I'd suggest this possibility.
Hematomas aren't generally dangerous, but can become a serious problem that could need a simple surgical procedure.