I have no clue as to the specifics of your son's case but, I would like to mention a couple of things. I historically go through what I call "seizure cycles" where I may go a few months without any problems at all, then I'll go thru a two-week period where I'll have three or four seizures (grand mal) a day.
Over many years, I learned to manually adjust my dilantin dosage to its MAX whenever a "seizure cycle" began.
Also, this zonegran stuff that my new neurologist has me taking has been fantastic (in my case). Not to say it would help in your son's case, but I would suggest it to his Doctor.