Usually, the first symptom of pyloric stenosis your baby vomiting small amounts of milk after feeding. At first, this may not be any more than usual. However, it gets worse and soon your baby can't keep any milk down. The vomiting becomes more severe and powerful. This is called projectile vomiting and it can be very forceful and travel some distance out of your baby's mouth. The vomited milk may be yellow or curdled and unpleasant smelling as it has mixed with acid in the stomach. Other symptoms may be:constipation, being hungry all the time, weight loss or lack of energy. Sometimes parents will notice a knot like mass seen on the abdomen just before vomiting.
Attribution: BUPA