Hello and welcome to the forums
Solabear has given you great advice regarding seeing your GP for a long appointment. That is what I did. When I booked I also said it was for a mental health plan so when I saw the GP they knew what it was for and I couldn't avoid the topic (I had booked a few appointments and chickened out of discussing my mental health). I also told someone I had booked an appointment so they made sure I went.
I see you have discussed some of the issues with your school and with the hospital. Have you heard of headspace. It is a youth mental health service and they have numerous locations around Australia. I went to one when I was at uni. I was also a part of CAMHS (child and adolescent mental health services) when I was young, but I wanted to try something different and headspace worked for me. There are also other local youth mental health services around, just google your local area and youth mental health (e.g. xxx qld youth mental health services).
As with uni you can cross that bridge when you get there and I'm sure you will. You sound determined and coming to the forums shows you are really trying to overcome your struggles and meet your goals. With Uni however they have services called disability services and if you have a mental illness you can join them. I did and they were really good. They can help you with academic care plans, counselling service, extensions etc. They also will not show any stigma and they will not say to your course coordinator why you joined disability services (for all they know you could have type 1 diabetes). Now with year 12 I would discuss with your counsellor regarding special consideration (I also did one at uni, as I was diagnosed with an illness the day before my exam and was worried I wouldn't perform). This allows the examiner to know you were going through tough circumstances and they can take this into account with their grading. Not sure exactly how it works but it is a good safety net. I would see if you could talk to your year level coordinator about it.
Hope some of this advice has helped.