See an eye doctor for one. Secondly you're dealing with perceptual issues and you should verify that your perception isn't faulty. See if you could find a light meter or use your phone in some way to gauge the brightness of your screen and of your environment. If you could look outside at a sunny day and you don't have to squint for a second because it actually hurts to see the brightness of the day then you might actually have a physiological thing going on.