Lamictal can be somewhat activating because it works on the depressive end of BiPolar (BP). When we first started it, our psychiatrists told us to give it to our kids in the morning. Once we went to divided doses (some in the morning, some in the evening), we tried giving it to them at dinnertime instead of bedtime. But both of my kids who take Lamictal still need something to help them sleep (Seroquel for my son, Zyrtec for my daughter).
What time are you giving Lamictal to your son? How much is he currently taking? How does his mood seem?