sitting in front of the screen not only irritates your eyes , but also can cause stiff neck which slowy leads to headache too.
blink your eyes every 2hrs for about 1min , get up from your desk and move about every 2hrs , increase your water intake, do not be empty stomach for long hours, try and have something to eat every 2hrs- eg. dates, almonds , etc..
Next Steps
If these basic things do not help, then consult your doctor