I work in front of the computer all day as well. I get double vision, sore neck and headaches also, especially when I'm tired or stressed (which is most of the time :) ). I have terrible eyesight -7.5,which I suppose doesn't help.
I also occasionally get dizzy after sitting for long periods of time in front of the computer.
My eye muscles are weak and they tend to do the opposite of being crossed, they fall outwards (I forgot the medical name), probably due to starring at the computer all day. Most eye doctors check for it but don't talk about it unless it's bad. I also see echoes in my vision, for example if i read white text on black background I will see faint lines wherever I look.
I had the same tests as you which came out clear.
I take more breaks while working, look outside,just get away from screens every 30 minutes or so and it seems to help. I also blink more which sounds funny but it kinda resets my eyes.
If it worsens I'd get it checked again but if you're fine a few days after not being in front of the computer then it may very well be that.