YOU SAID:

I am supposed to be doing homework

INTO JAPANESE

私は宿題をしているはずです

BACK INTO ENGLISH

I should be doing my homework

INTO JAPANESE

私は宿題をしなければならない

BACK INTO ENGLISH

I have to do my homework

INTO JAPANESE

私は宿題をしなければならない

BACK INTO ENGLISH

I have to do my homework