In fact, considering your son's mood swings and affective disregulation, I think it'd be wise to look at adding a mood stabilizer- something like Depakote- or a mild antipsychotic like Abilify, to control the mood disruption (trust me, for this kid on those drugs, there will be mood disruption) and conceivable hypomania/mania resulting from the combined impact of two powerful pick-me-up drugs (sertraline and amphetamine).