Suggest Remedy For Gag-reflux And Vomiting Sensation After Eating

My 11-year old son has complained of a gag reflex-like symptom when eating the last two days. Tonight - hours after eating a very small dinner - he is uncomfortable and says that when he breathes, swallows, or chews anything he feels like he s going to vomit. He s carrying around a bowl spitting in it and is visibly uncomfortable. No fever and I looked in his throat, which looks fine to me (no redness or inflamation). What should I do?