I'm a little concerned with the way that your vet is treating this. Have you had any tests run? Giving medications without a proper diagnosis leads to a) medication resistant diseases b) delays proper diagnosis and treatment c) ends up with unnecessary medications in their system.
Assuming that it is asper, Aspergillosis very frequently occurs at the same time as a bacterial infection. Giving some antibiotics and seeing if they work won't tell you if there is a bacterial infection because different bacteria respond to different drugs. Lupin needs a culture and sensitivity test to detect and identify bacteria. There are also three different tests for asper. My African Grey, Judy, has asper. Two of the three tests have been negative. We're waiting for the results of the third. The results are only to give us a baseline. Judy definitely has asper because the vet has been able to see it in the things coming out of her nose.
Judy's case is really severe and has gone untreated for a very long time, so don't get too worried about Lupin if you read her story. You've caught it quickly. With Judy, it went untreated by her previous owner. After I got her, it was misdiagnosed and mistreated by the first vet I took her to. He gave her antibacterials and antifungals, but they were broad spectrum and didn't treat the bacterial infection she has or the asper. Judy ended up having a seizure that has limited the mobility in her foot and possibly her wings. Another doctor diagnosed her with a foot injury. I finally got her to a good vet and she's now on the proper anti-fungal for the asper and we're waiting on the results of the culture and sensitivity test before treating the bacteria so that it can be treated properly. At this point, Judy's case is so severe that we may not be able to get rid of it, just manage it. My vet has also said that sometimes it takes more than one anti-fungal to keep it under control. It depends on the severity, the bird's immune system and probably the fungus itself. I urge you to make sure that Lupin gets properly treated and tested while it's still early.
As far as keeping it from coming back: no peanuts, no walnuts, no beddings made out of shells, no wild bird mixes, no pet grade nuts and seeds of any sort, especially sunflower seeds. No letting food mold in the refrigerator. I realize the climate there makes it very difficult to control mold in your house, but keep it under control the very best that you can. The molds from food and in a house are probably other types and aspergillus is the only one known to reproduce in the sinuses of a parrot, but why take a chance?
I wish you and Lupus the best. Remember that you are his voice and his advocate. Don't feel bad pushing the vet for more or getting a second opinion.