[dlandis]

"I do not wear my glasses while at the screen, as it's close enough that I don't have any issues."

This could be the problem, especially if you are close to 40 years old. You may be starting to develop presbyopia, which is typical. In the early stages you can still read and focus on closeup things fine, so you may not realize it is starting, but in the background your eyes are, in fact, straining a lot and causing headaches.

[Night_Thastus]

I'm not in my 40's, but I'll keep that in mind, thanks.