Yes, there's no doubt that stress (which may not be evident from an 'objective' point of view) could bring about such reactions. It's also entirely possible that his emotional sensitivity is influenced by the collection of medications he takes - these can promote emotional instability.
Apart from the crying, how is he doing? Is he functioning well within the family? Does he have friends and, if so, is he doing well with them? How is school going for him? If, at the so-called bottom line, he is mastering the demands of his life, it is entirely possible that you are witnessing the side effects of medsthough this would only be true if he is taking these medications on a pretty regular (as opposed to intermittent) basis.