Kame No Tabi (A Turtle's Travels)

I have been getting headaches more and more frequently at work, so I wonder if maybe I need reading glasses. I am wondering if there is any way to tell if your headaches are from reading while needing glasses or from something else. I wonder because my vision never goes blurry (so I think I'd pass an eye exam just fine) but the headaches persist, and they seem to happen whenever I'm at work (where I do a lot of reading and looking at a computer screen) Does anyone have any suggestions/ideas?