Hi Jessie ,
A big Aussie welcome to Susan's family. It's good of you to drop in and say "Hi". Hope you like it here, and you stay for a while.
There is a mountain of information, resources and friendship waiting for you here, you just need to jump in and start talking.
To answer your question on what to do next; finding a therapist who is experienced in gender issues would certainly be the best start. It's impossible to keep pretending this is not happening. That's called denial, and the longer you let it survive, the longer it's going to take to heal, and the more damage it is going to create for you.
It may be best to start with your school or college nurse/counselor. They should be able to advise you on the best way, for your circumstances, in which to go. Do realise GID (gender Identity Disorder) is a recognised medical condition. At some point in time your parents will need to know this and that it is treatable. Your therapist will best advise you on how this should be done.
Looking forward to hearing more of your story in time to come, but in the meantime, be safe, well and happy.
Lotsa huggs
Catherine