Dry eye symptoms on a computer are typically caused by reduced blink rate. When you remember, just do 5 deliberately exaggerated forced blinks.

Other causes are

Blepharitis, dandruff of the eyelashes, use a medicated lid wipe like Blephaclean or TLC Lid wipes. Good lid hygiene is the key.

or Meibomian Gland Dysfunction (MGD) aka Posterior Blepharitis. Blocked meibomian glands prevent the oily layer of the tears from forming allowing evaporation of the 'water' layer. If you have thickened lids this is likely to be the cause. Hot compresses unblock the the meibomian glands. You can make your own with a wet flannel heated in the microwave. You can buy products like an Eyebag. Look on YouTube for instructions.

You'd really need to see an optometrist to find the cause, but these are simple self treatments.

You can of course treat the symptoms with artificial tears. Systane Balance for example will lubricate your eyes and has a duration of action of typically 2 hours though this can vary markedly.

I doubt whether your ocular symptoms are related to anything else. They are common symptoms for a man in his late 60s.

On a side note. If you don't feel Gabapentin is doing you any good don't take it.

Your trunk area. And this is purely speculative. I wonder if you have an intercostal problem? Possibly a low level form of intercostal neuralgia? Nerves can become hypersensitive. I note you are lifting weights. Maybe worth some self investigation.