I would be concerned that maybe the dose is too high if he is just now sleeping too much on it. However, I had that side effect when I first started it at 500mg, it went away. And yes I have gained a little weight but I have managed to not have a seasonal manic/mixed/depressed episode this spring which is a very important thing to me. There are so many things you have to consider with this illness and the different meds used to treat it. A good talk with his dr is a good place to start. I wish you and your son the best.