When i read and study too much before exams, i feel this really bad pain under my left eye brow, it keep coming and going. why is dat?

The muscle that : Moves the eye down runs up near the bone of the brow. Straining that muscle could do it! try propping your book up so that you are looking more straight ahead.

Try this: Try some low powered reading glasses. It is likely this discomfort is from eye strain. If the glasses do not make the discomfort cease, then make an appointment with an eye doctor to find out what's going on.