Our twins have reflux. I would say try to keep him upright for at least 20 min after he eats. Our babies are bottle fed. Swings and chairs work well to keep them upright after they eat and to sleep in so they aren't uncomfortable. Also, if it gets too bad make sure to ask about a possible milk intolerance (as in dairy, maybe try cutting it out of your diet) and possibly Zantac if it gets too bad.
Is the baby gaining weight well?