What you eat can. Breast milk won't make babies gassy usually, and most tolerate straight breast milk very well. However, there are certain foods that are famous for causing gas and bloating if mom eats them, then breastfeeds: cabbage, spicy foods, pepper, onions, garlic, caffeine, broccoli, cauliflower, carrots. I've had parents figure out almonds, tomatoes, and such. Scout recent meals and take notes.
Probably not. Breast milk is by far the best nutrition for your baby. It is rare for babies not to tolerate breast milk. Gassy? Many babies get this. Maybe it is air swallowing? Are you burping as you should? Reflux is not a process of the milk but is an anatomical issue with the way the baby is made. See your baby's doctor and consider a lactation consultant for further advice and treatgment. Workable.