breast or bottle feD?
breastfed - possible overactive let down
bottle fed - possible too fast of a flow on the nipple. try a slower flow.
other things to try:
feeding him with his head more elevated
taking the bottle (or your nipple) out of his mouth every few sips or few minutes or however often, he might be eating to fast.
and if that doesnt work or you are really worried and want an answer ASAP then ask your dr. Lincoln chokes a little on my milk sometimes when he is eating too - when he is eating too fast. happens more often when I give him a bottle of breastmilk then when I feed him from the tap