Hi, Alana!
I am on the shorter side, too, so I know how you feel. If you want to start a portfolio, then you will need to arrange "test shoots" with local photographers in your area. Agencies aren't going to help you with that so for now you are on your own. At your height you can do commercial/print so that is the type of work your portfolio should reflect. Of course you can also do swimwear or lingerie if that is your thing.
Finding a photographer can be as easy as Googling it. For example, "photographers in los angeles" will get you a bunch of results so try that but with the area you're in. Actually here on Modelfolios, there are one or two members that are photographers from Australia. I will post here again in a minute...I'll check my past posts with them and get their profile names so you can hopefully correspond to them.
Since you're starting out, don't worry about paying for a shoot. Doing test shoots as an exchange of services is a good place to start out. Later on if you're looking for a specific theme then you can look into hiring a photographer and paying him/her.
Be right back!