YOU SAID:
I can't believe I'm doing this.
INTO JAPANESE
こんなことをしているなんて信じられない。
BACK INTO ENGLISH
I can't believe you are doing this.
INTO JAPANESE
あなたがこんなことをしているなんて信じられない。
BACK INTO ENGLISH
I can't believe you are doing this.
Well done, yes, well done!