It is just possible that you are suffering from refractive error
for which you should undergo a refraction
and get the glasses for your visual correction. If you are above the age of 40 years, you may need presbiopic addition also to your distant vision glasses. This should solve your problem. However, you can use some lubricating eye drops to give a soothing effect to your eyes.
You should try to assess your thresh-hold for working on computers and try to take rest for a few minutes before the thresh hold is reached. Good diet and good hygienic habits for eye will also help in improving your general health. You should get your blood pressure checked to rule out hyper-tension.