Ayahuasca wrote:I've been getting mild headaches...
Oftentimes headaches are due to muscle tension. They're generally termed muscle tension headaches. I work on the side as a massage therapist, so I have some expertise here...
Sitting in front of a computer, especially if a person leans back in an office chair, and rounds their back and shoulders forward, the posterior cervicals (muscles of the back of the neck) can become tight and shortened from having to level the head. Pain, and headaches, from this usually radiate from the suboccipitals at the rear base of the skull. Also, if the posterior cervicals are being chronically shortened, then the anterior (front neck) muscles could be getting overstretched--and this causing headache-like pain, too.
Sitting up is, I think, the best global solution. And by sitting up I mean holding your head over your shoulders. (If your chin is jutting, then your head is probably not centered over your shoulders). Your head weighs (on average) 10-12 pounds, and for every inch you're holding your head out in space over your shoulders, you're asking your neck muscles to support an additional 10 pounds (more or less).
Another big factor in computer-related pain is having your arms rest too high, causing flexing/shortening in your shoulder/neck complex. Your shoulders, ideally, should feel like they're naturally drooping while typing. Raising your chair might help with this.
A great stretch for the back of the neck is the Yoga Bridge pose. You lay on your back, knees bent, feet on the floor, your fingertips just able to touch your heels. Then you push your hips toward the ceiling, forming a line (at 45 degrees or so) along your thighs, abs, and torso. You hold the position for about three breaths. Don't turn your head in this position.
I find it useful.
Ayahuasca wrote:I know it's not my eyesight because I wear glasses and my eyes were tested quite recently. I don't have any problems with focusing.
I recently heard of a study stating that when people watch television or sit in front of a monitor, they tend to blink too little. On average, the eyes blink 20 or so times per minute. When in front of a TV or monitor, testees only blinked 8 times per minute. Blinking massages the eyes.
I've been trying blinking breaks when I'm at the computer. 
You can't change a tiger's stripes,
but you can avoid its teeth.