YOU SAID:

do you need a pen why would i need a pen i'm not sure

INTO JAPANESE

ペンが必要なのですがなぜペンが必要なのでしょうかわかりません

BACK INTO ENGLISH

I need a pen, but I do not know why I need a pen

INTO JAPANESE

私はペンが必要ですが、なぜペンが必要なのかわかりません

BACK INTO ENGLISH

I need a pen, but I do not know why I need a pen