YOU SAID:

I really should be doing my homework.

INTO JAPANESE

私は本当に宿題をしているはずです。

BACK INTO ENGLISH

I should be doing my homework.

INTO JAPANESE

私は宿題をやっている必要があります。

BACK INTO ENGLISH

I'm doing my homework.

INTO JAPANESE

宿題をしてるの

BACK INTO ENGLISH

I'm doing my homework.