They have to scrape some of the tissue for a culture, even inside the nostrils. No two ways about it. Even if it's a fungal infection (which it sounds more and more like), they have to know what kind so they know how to treat it. IF you get a bunch of head scratching and "I dunnos", you might...
Oh, my! How awful! I am so sorry you had to go through that! Hope the next one is better! PM me if you feel you've wound up on your own with this. There will have to be skin samples and bloodwork. There's no other way to diagnose. I'm still betting it's fungal and easily taken care of.
Mad Hatcher, this could be a fungal infection. Not enough info in your post. Do you have a vet? If so, would they be willing to take a skin scrape for you and send it to your state lab? That's really the only way to be sure. That said, I'll warn you that it's very difficult to find a vet...