It is unfortunate that our society glorifies the intellectual brain, and expects students to develop themselves in an unbalanced and harmful way. Especially when in school, we become very conscious of the suffering imbedded in this broken system. Nevertheless, if you wish to pursue a path in life that uses the intellectual center, it is necessary to develop it.
There is nothing wrong with the development of the centers. But we create problems for ourselves when we develop them in an unbalanced manner, or when we exert them beyond their capacity.
In that sense, pay attention to what your body is telling you. Sleep is important for learning. You will develop the centers (including the intellectual center) much more effectively if you make skillful use of sleep. Reading a book will make you tired. That's not a problem; it's a signal. Rest. If you try to exert the intellectual brain, you will only create confusion (or worse), just like if you exert your motor brain without resting, you can cause damage to your muscles.
There was even a recent article about the importance of sleep for learning published this past week in the New York Times:
http://parenting.blogs.nytimes.com/2014/10/16/want-to-ace-that-test-get-the-right-kind-of-sleep/
So don't neglect it.
And in the meantime, it also helps to work on developing the other centers. When you're not too tired from studying for your tests, read the sections, "The Doubles,", "The Cardias," and "Practice" in this chapter of the Perfect Matrimony:
http://gnosticteachings.org/books-by-samael-aun-weor/the-perfect-matrimony/949-the-flying-serpent.html
It will help develop your emotional brain as well.
And don't stress too much.