Being a baby is complicated. Their little bodies and digestive systems are changing constantly as they grow. And with all of those changes, your little baby can easily become gassy, with fussiness following next. Everything from inhaling air during feeding to the stress of their environment can produce excess gas. You can reduce these episodes by making sure the bottle is correctly positioned with baby's head elevated above their abdomen, and feeding in a calm place.
Another reason for fussiness can be food sensitivity. Moms of breastfed babies can try changing their own diet to see a difference in how their babies feel. The American Academy of Pediatrics (AAP) recommends cutting down on milk products or caffeine, and avoiding spicy or gassy foods, like onions or cabbage. If that doesn’t work, then go back to your normal diet and consult your baby’s doctor.