Aus. Post have some information on their site about the impact of COVID-19 on shipments that you should read.
There's some more background info at the ABC. And this article (warning - leads to news.com.au, a Murdoch garbage site) - that explains why some parcels being sent from Victoria to Victoria are currently being processed through Sydney.
In short, they are busier than Christmas, and substantially so.
We have also been advised that Australia Post are not currently scanning parcels as frequently as normal during the parcel journey.
This means that you will get fewer notifications, and that it may appear that parcels seem to be 'stuck in the system' - often for several days - without visible progress.
It seems currently there are events when we book the shipment and when we deliver the days' parcels to Aus. Post., then nothing much further until the parcels reach the distribution centre, or even until they are on board for delivery.
We are regularly seeing 5 to 7+ day transit times for regular parcels, or even longer for remote destinations. Express is of course much quicker still, so choose that if you're in a rush.
Unfortunately we don't get any more information than you can see for yourself via your tracking number, and we have found it is pointless to call Aus. Post about your parcel if it is anything less than a full 7 business days (and even then the message is usually just to continue waiting).
Unfortunately, during these exceptional times, we all just have to be patient! Thank you for bearing with us!