I had head aches at first too. I got my glasses at 19 when I realised that the words on the computer screen were bouncing up and down lol. I was working as an archivist so I spent a lot of hours reading. You'll also notice that your eyes will probably change within the first year, and maybe even a few years. After I year I had to get my prescription updated, which was fine because I had broken my frames anyway! You can reuse your frames though if they are in good shape.
The reason you get your headaches anyway is because your eyes are relaxing finally. They are used to being all scrunched up trying to make things look clear. I desparately need new glasses but can't afford them right now with tuition being due soon :(.