Hi josh
In Victoria 'possession' defined in reference to a drug can include the physical control or custody of a drug to the exclusion of all others not acting in concert with the person.
It can also include a drug being on premises or land occupied by a person or a drug used /enjoyed/controlled by a person unless it can be proven otherwise.
As a guide, in Victoria a small quantity of methylamphetamine (ice) = 0.75g & a traffickable quantity = 3g.
A police cautioning protocol applies to cannabis & heroin 1st time offenders but as there is no mention of its' application to a person in possession of methylamphetamine. I would suggest that you contact a lawyer ASAP.
Regards