M.P.
Do you keep him semi-upright while you're feeding and for at least 30 minutes after. Is his head higher than his bottom when he's lying down? My grandson suffered from reflux and slept much better in his car seat because it did keep him more upright.
What happens when we lie down is the acid is then caused to flow up out of the stomach due to gravity. By being more upright gravity helps keep it in the stomach.