Ok, it seems that you are quite interested in reading books, good for you anyway. So, you should know that our eyes also require some time to rest and relax, if not, they would simply get sour, painful, and stressful. So, now what you should do is to take breaks at intervals, also, you could try some teas which could relieve your stressful eyes. In addition, try to get more rest and take more vitamin pills. If necessary, you also could get some eye drops. Hope you recover as soon as possible.
Well, close your eyes at soon and keep good mood which is good to reduce eye pain. Then do some eye exercises that can relax the muscles around eyes. But after a long time reading, your eyes feel pain and this is not only becasue of the muscles tired around your eyes, but also eye nerves and blood circles around eyes. So doing some eye exercises can help you recover normal blood circles and reduce eye nerves tired conditions. By the way, you also can apply cucumber slices on your eyes and you may feel cold and comfortable at soon.
There are many ways for you to relax the muscles around your eyes when you feel the eye pain a little. You could just close your eyes. Then you could look at the far scenery through the windows in the tall buildings. You will find that your muscles will be in the relaxed state. You could also use the warm compress to make your eyes feel relaxed to some degree.