Am I underpaid?

I am working part time in a gelato shop in Sydney and when talking about my wage with people I was told that I might be underpaid. I don’t know if this a relevant info but the gelato shop belongs to an international company. I am paid 24.8$/hour no matter what day or what time of day it is (i usually finish my day around 12am or 1am) except on public holidays where I am paid 6$ extra per hour. Some australian people said that they thought it was illegal to be paid the same on weekends and during the night. Do you guys think the same? What should I do about it?