Newborn threw up his milk

Sesme • ✨Mama Bear✨💝
My newborn has been taking his bottles well all day and burping and hasn't been fussy and making all his bowel movements and wet diapers. And all of sudden he threw up his whole bottle of milk, can anybody tell me why this is happening ?? He's taking Gerber Good Start Gentle btw and 3oz every 3 hours