The most common reason for a baby not burping after feeding is the mother's milk, which is usually high in lactose. However sometimes babies have reflux or spit up more than what will come out while eating.
While babies can't tell you about their discomfort, here are some signs that your baby might not be feeling great: crying a lot, appearing restless and uncomfortable, moving his head from side to side, arching his back with bulging eyes and tense neck muscles.