At three months, a baby’s digestive system is still developing. This immaturity can lead to reflux, causing them to spit up. If the baby is put in a position that puts pressure on their stomach, it can lead to discomfort and spitting up. Keeping the baby upright during (as well as after) feeding can help. If the baby is unwell, such as having a cold or other infections, it may affect their feeding habits and lead to spitting up.
Yes I’ve experienced the same thing with my little girl. Bringing up the feeds with projectile vomiting. It started after her first set of vaccinations. It is reflux. Been prescribed gaviscon and it’s been a few months using it for my little girl
Could be any of those or any other reason. Could also be pyloric stenosis that doesn't usually show up until they are eating more/quicker.