Is your doctor in NZ? If so, ask him/her. In the USA diabetes medication has to be prescribed not sold over the counter.
Also, insulin is not safe to use if you have not been trained in how to use.
For now your best approach would be to monitor your blood sugar (you can do this with a blood sugar testing kit, they are available in pharmacies, and come with complete instructions.
You can also help by making sure you limit how much carbs (and particularly breads, pastas, sweets, softdrinks you consume), and making sure you get at least 30 minutes of moderate exercise a day.
Work with your doctor. Best wishes.