The kind of work God usually calls you to is the kind of work (a) that you need to do and (b) that the world needs to have done. If you find your work rewarding, you have presumably met requirement (a), but if your work does not benefit others, the chances are you have missed requirement (b). On the other hand, if your work does benefit others, you have probably met requirement (b), but if most of the time you are unhappy with it, the chances are you have not only bypassed (a) but probably aren’t helping your customers much either.
....Neither the hair shirt nor the soft berth will do. The place God calls you to is the place where your deep gladness and the world's deep hunger meet.

Frederick Buechner. WISHFUL THINKING: A SEEKER'S ABC