What type of seizures and where are they located? Any chance you are seeing partial seizure activity? Is he taking only Lamictal?
My son's story is long and not really relevant to your son so I'll skip the boring details, but after my son stopped his other medications he continued on the Lamictal for quite a while. We thought it was helping but I have to admit that since he stopped taking it, his anxiety -- which prevented him from leaving the house for years -- has pretty much disappeared. I was never quite sure if that was because his brain healed, because he matured, because the Lamictal was causing anxiety or all of the above.
I have some concern that people are looking for psychological explanations for what very well may be neurological issues that your son is continuing to have.
I have a friend who has temporal lobe epilepsy and has been seizure free for the first time on Topamax and Lacmital but he had to add Lexapro for the depression and anxiety. There is the theory out there that controlling seizures causes depression and anxiety. Or maybe the drugs do. When I was diagnosed there was the psychological theory that people with controlled seizures had increased anxiety and depression because we sat around worrying about when we were going to have another seizure. I assure that theory is hogwash.