YOU SAID:
I don't know why I am doing this anymore.
INTO JAPANESE
なぜ私はこれをやっているのか分からない。
BACK INTO ENGLISH
I do not know why I am doing this.
INTO JAPANESE
なぜ私がこれをやっているのかわかりません。
BACK INTO ENGLISH
I do not know why I am doing this.
You've done this before, haven't you.