Another thought... has there been any itching, scratching, twitching, laboured breathing, or anything else notable?
The way the wound looks, and the way it isn't responding to antibiotics, has me considering ciliates. If it is, there are a few things that could help externally, but really only one difficult to find med that would be helpful internally. We should still give some time for the Neomycing & Triple Sulfa to work, but considering how difficult it is for you to get things, you might want to start looking for sources for Formalin (relatively easy to find) and Chloroquine (relatively difficult to find and not a fish med; used for malaria), in case there still isn't any improvement with the change in meds.