What Could Episodes Of Lightheadedness, Confusion And Headaches In A Child Indicate?

Hi! I have a 12 yr old son, active in football, basketball and baseball. He is going thru some growing right now. He is presently experiencing some "episodes" of light headedness, confusion, sometimes headache and sometimes stomachaches, a couple times a week. always at end of school day. Never at home. Seen pediatrician several times, has CAT scan with and without contrast, it was neg. He thought migranes?? and now maybe bld sugar levels in question?? What are your thoughts?