[susan53]

I had never been Australia before but (now) I have been Australia (for 5 weeks).--> I mean that now I have live in Australia for 5 weeks and this is the first time for me in Australia. So what is the correct sentence?

"had been" sounds strange here. You might say :

This is the first time I've been to Australia. I've been here (for) 5 weeks now.

This is my first visit to Australia. I have never been here before. or I was never here before (which answers your other question)

"had + past participle is used to talk about a past event which happened before another point in the past so isn't relevant here. You might use it to say eg :

I had never been to Australia before 2008, but since then I've been there 7 times!