I used to get a lot of headaches as a child. My mom says it's because I used to read non-stop but I'm not so sure. Eye strain is in fact one reason, but there are many more such as sinus issues, food allergies and of course stress and diet.
Feverfew is a popular herbal remedy. Go get some if you're prone to bad ones. And according to one of my girls in pain this morning, this remedy works wonders too:
*Note: Stay clear of Feverfew if you have seasonal allergies, because just like chamomile (something that many are unknowingly allergic to) it can cause reactions similar to that of ragweed/pollen etc.