PR expiry and Resident Return Visa

As you have been away from Australia for so long they have only given you a temp visa so you can enter the country. You will then have to contact them and more than likely reapply.
Just remember that with the coruna virus scare you may not be allowed to enter the country either whilst borders are closed.
I suggest you try contacting the Embassy for information.

you mean after entering the country I have to reapply for PR again?

I concur with Stumpy. You only got 3 months because you did not show strong ties to Australia and only entered the country once since you were granted the Residency in the first place. If you had stronger ties to Australia you could have been granted a year for residency return visa. I had this granted to me as I needed to go to Canada, expected 3 months since I did not meet the requirements for a 5 year residency renewal visa.

At any rate, I commented on your other email and suggested a migration agent who may give you advice.

Good luck
Norman