Why should you be motivated? School work can suck ass. Maybe you dont find it easy to do. Maybe your teacher is a bitch who doesnt care about you. Maybe you cant concentrate. Maybe you rather be off doing something else. So, why should you be motivated?
Maybe the problem isnt the schoolwork itself, maybe the problem is you. You cannot focus, can you young Luke? Use the force Luke. Focus!
You could try doing just a little bit, then taking a break. Then do a little more. Then taking a break. And so on. Too much work, and too little play, isnt fun.