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
That didn't even make that much sense in English.