Your probably getting eyestrain. 3 tricks I use to fix this 1) sit farther away from your screen and turn on a light or two 2)after every match, pick an object at least 20 ft away from you and look at it for at least 30 seconds. Blink normally while you do. 3)contract every muscle in your face at once. Like your making the bitter beer face. Hold it as long as you can. It's weird but this helps even if your already feeling the headache.