Be careful about tree tree oil… it was wildly popular til they found many issues and reactions to it.
San Francisco State University:
Common herbs that are potentially dangerous for use in animals
Pennyroyal (very toxic to dogs and cats)
White Willow bark (salicylates may be toxic to cats)
Garlic (Heinz body anemia)
Tea Tree oil (VERY toxic to cats and small dogs)
Ma Huang (cats have idiosyncratic reactions)
Comfrey (cause liver damage)
Hops (in greyhounds
If the antibiotics cleared it up, then it almost has to be bacteria related or it would not have cleared up. BUT could be allergy start and then bacterial developement.
If you can, go to a university vet school for exam so they can help look at diet and other issues, as well as skin scraping etc.