Unless it's a growth spurt, it can be a sign of reflux. The sucking action keeps reflux down. Silent reflux, meaning there is no or little spit up, is like when you get stomach acid in your throat. It tastes nasty and feels like heartburn. Sometimes a pacifier will work too, but some kids don't like pacifier - or the milk keeps the icky taste down. Certainly we are not doctors, and it could be something else. Reflux is often worse in the evening, but that wasn't the case with us. Even with Rx formula we had to use gas drops before and after every feeding, burp frequently during feeds - like every 10 swallows, and not bend her over at the stomach, keep her upright for 20-30 minutes after each feed (think swing/carseat).