I'm having trouble with my employment?

Sorry, but for a 20 year old, you seem incredibly naive. Your birth certificate indicates your nationality. You are an Australian. Although you are entitled to British citizenship, it does not happen automatically. You have to apply to the Home Office. You would have problem applying for a British pport because the way things are, you are not British. The fact your only pport is an Australian one would be regarded as suspicious by employers insofar as you have no actual proof of your entitlement to work in the UK