Hi Julie,
I was 10 yrs. old when I started having migraine headaches that lead to sz. My neuro did a special eeg on me where they flashed different color strobe lights one at a time and they found that certain colors were triggering sz. and migraine headaches because I was photosensitive. It's also been proven that certain sounds can cause migraines and sz. as well.
I started taking depakote when I was 16 yrs. old and it never caused me to have headaches. I ask myself if all of this isn't hormone related because your son is beginning to go through puberty. You might want to have him start taking vitamin B12 once a day to see if that helps. I wish your son and you the best of luck and May God Bless You and Your Family!

Sue