Fetching details from the dictionary...

week before last
先々週の会議の内容を思い出せない。
I can't remember the contents of the meeting from the week before last.
先々週に買った本がまだ読み終わらない。
I haven't finished reading the book I bought the week before last.
先々週から続いている咳がやっと治った。
The cough that's been continuing since the week before last finally healed.