Classic eye strain symptoms from using any monitor including the old school CRT monitors. I used to live behind a computer for work during the CRT monitors era and my eyestrain got worse and worse as the years went by.
The number one cause is fatigued eye muscles including the forehead muscles. Basically from struggling to see things clearly where clarity does not exist. They get weak and fatigued and sensitive.
Its a MUST to wear proper prescription eyeglasses for computer use even if you think your vision is pretty good. They let the eyes relax.
But the only way I could get rid of the pain long term was to not look at computer screen.