Your negative HIV test 8 weeks after the apparent exposure (assuming you had sex during the period you don't recall) prove you did not acquire HIV at that time. Symptoms are never a reliable indicator of HIV infection; they suggest the possibility of an oral yeast infection, but other things can cause the same symptoms, and oral yeast infections can occur in people without HIV. I speak from experience; I have had it myself.
The Australia sexual health centres comprise one of the world's most expert networks of STD/HIV clinics. Although I am not familiar with the Canberra SHC, I am sure you can rely on their expertise. If they have reassured you, you have no worries.
Best wishes-- HHH, MD