My son is 8 and is non-salt wasting.  He gets what I think are migranes also.  They usually  happen later in the afternoon, between 3 and 5:00.  A couple of years ago, this subject came up on the board, and one of the person’s responding said that someone suggested juice in the afternoon.  I thought this sounded odd but was willing to try anything.  So now, my son, takes juice to drink at school inthe afternoon and it has really helped.  It hasn’t elliminated the headaches, but they are fewer and farther between.  Give it a try.