Burning out is a common problem on any test prep/review.
Couple points to keep in mind:
-Make sure you are benefiting from your time. Remove distractions by removing yourself from an environment of distractions and/or complete other tasks you know will linger in your mind (errands, cleaning, etc.) before you begin studying for the day
-There is a need for "brute force" studying at time (forcing yourself to study). This is normal, but it should not occur every time you need to study.
-Take breaks from studying. This is very important. The mind is like any other muscle, it needs to relax after working hard. There's no shame in taking a day off here and there to unwind, go out, etc. That being said, you still must give prep its due time.
Best of luck,