I once had a similar experience. My eyes would also twitch at random times during the day. I realized that this was because I was reading at night with only my nightstand lamp on. Make sure that there is an adequate amount of lighting when you read, because the aftereffects will carry into the next day. Also, if you spend a lot of time online, the computer screen could have something to do with it. People at my old school were having eye problems and we realized that it was because the monitors were tilted at a weird angle and the lighting flashed/twitched every few seconds.
Try taking a break from reading for a while
See an eye doctor to see if you need glasses or a stronger perscription if you already have them
Try wearing sunglasses when you read. Seriously, it works. Sometimes the stark contrast between black and white hurts the eyes so wearing sunglasses makes it easier to look at.
Maybe you watch too much TV or are on the computer too much. Staring at a screen for hours a day will make your eyes sensitive too.
it depends on what you're reading. if you're reading off a computer screen, odds are that you aren't really blinking enough..and that's what's making your eyes hurt. Either that or try taking breaks from looking at the screen and stare at a something like a blank wall for a few minutes (just to give your eyes a bit of a rest).
But it is good to get your eyes checked regularly.