YOU SAID:
I have a stomachache, so I will take a day off today.
INTO JAPANESE
お腹が痛いので、今日は休みます。
BACK INTO ENGLISH
I have a stomach ache, so I will be absent today.
INTO JAPANESE
お腹が痛いので、今日は欠席します。
BACK INTO ENGLISH
I have a stomach ache, so I will be absent today.
That didn't even make that much sense in English.