Hello again! If there's nothing following the statement, you wouldn't use a past perfect continuous. You'd only use a past perfect if this period led up to a significant point e.g. "...I had been cooking cutlets in a restaurant every day for three months when suddenly I had a revelation." (or some other event happened). In the absence of another key point of reference ( i.e. what brought those three months to end), you would use a past tense rather than a past perfect: either 'I cooked' or 'I was cooking'.

I wasn't sure which tense to use because from one hand it mentions a continuous period of time and from the other hand i don't have anything to say after everything i have mentioned. Thank you guys you have cleared up everything for me! I wish I could help you in turn.

Your sentence feels incomplete because it doesn't mention anything else that is related to the fact that you had been cooking. It would sound better to me if you use simpe past: "When I was in Australia, I cooked cutlets in a restaurant every day for three months."