Butterfly-that sounds like classic PANS to me. I think you're exactly right. No, you do not need another sudden onset of symptoms to be diagnosed or treated. (Some PANS patients don't even have sudden onset.) Many doctors will diagnose based on medical history alone, as you said, or if you are interested in being tested, the Cunningham Panel by Moleculera Labs is considered standard for PANS. They do run tests for those living outside of the US, but the test is costly, usually around $900 (and that was for patients in the States, I have no idea what it would be in Australia). Here's their site, if you want to take a look at it. https://www.moleculeralabs.com/ There's a neat video on their site that shows exactly what's going on with your immune system and brain in PANS, too, if you are interested in that.
To get treated-I saw above you said there is no PANS doctor where you live. Not all doctors that treat PANS list it on their site-one of the doctors that has treated me specializes in autoimmune diseases, but still had experience with PANS. You might call around to integrative medicine doctors or naturopaths in your area-there seems to be a higher amount of doctors willing to treat PANS in the integrative and holistic community. If that fails to yield results, there are some PANS doctors that will allow you to do Zoom or Skype visits. Usually they want the first visit to be in-person, but if you called and told them about your situation with the state borders, they may make an exception.
As for your actual treatment options, here's a really good overview from both the PANDAS Physicians Network and PANDAS Network that outlines what most doctors will go by. Some doctors don't follow these guidelines exactly, but these are the general options most of them suggest to their patients. (There are a lot of alternative treatments out there, too, in the holistic or integrative communities. Google search turns up a lot of these options if you're interested in looking into them.)
https://www.pandasppn.org/treatment/
https://pandasnetwork.org/understanding-pandas/treatment/
Also, I saw your question about getting tested for the trigger posted above. It's extremely likely that if you're still having symptoms, whatever bacteria or infection caused them is still present in your body, even if you have no symptoms that would traditionally be associated with that infection. (E.g. as far as I'm aware, very few PANS/PANDAS patients get fevers, and some of them do not present with a sore throat or rash with strep and scarlet fever. They just have a flare in their PANS/PANDAS symptoms). Here's a page from PANDAS Network that explains some common infections associated with PANS, and the tests that might be run: https://pandasnetwork.org/understanding-pandas/diagnosis/ Some PANS/PANDAS patients request strep titers tested, even if they have no traditional strep symptoms. Not everyone with PANS has high strep titers though, so it isn't a foolproof test. It can be a starting point, though, especially if the patient improves after antibiotics are given for high strep titers. As Cmac said, it's very worth looking for environmental triggers as well-mold, for instance. However, the way you describe your 3 symptom flares makes me think that your main PANS triggers right now are probably infectious/bacterial.