this we call as computer vision syndrome
few changes in ur workstyle can make u feel better.
1) u forget to blink frequently when u r on computers so take a short break atleast every 20 min like keep ur eyes closed for a second or shift ur eyes away from the screen for few seconds.
2) its better to have ur computer at a lower level than ur eyes.so ur eyes get exposed less to the bright light.
3) make sure the air conditioner doesnt blow straight onto ur face. air conditioners too dry ur eyes.
4) in addition apply lubricating drops thrice a day.