YOU SAID:

My jaw hurts really badly and so does my lower back. Why is that?

INTO JAPANESE

私の顎は本当にひどく痛いので、腰も痛いです。それはどうしてですか。

BACK INTO ENGLISH

My jaw hurts so badly that my lower back hurts too. Why is that?

INTO JAPANESE

顎が痛くて腰も痛い。それはどうしてですか。

BACK INTO ENGLISH

Why not?

INTO JAPANESE

どうしてダメなの？

BACK INTO ENGLISH

Why not?