Symptoms of pyloric stenosis usually appear within 3 to 5 weeks after birth. Pyloric stenosis is rare in babies older than 3 months. Symptoms include: 
Vomiting after feeding. The baby may vomit forcefully, ejecting breast milk or formula up to several feet away. This is known as projectile vomiting. Vomiting might be mild at first. But over time, it becomes more severe as the pylorus opening narrows. The vomit may sometimes contain blood.
Persistent hunger. Babies who have pyloric stenosis often want to eat soon after vomiting.
Stomach contractions. You may notice wavelike contractions that ripple across your baby's upper stomach area soon after feeding but before vomiting. These contractions are part of the digestive process known as peristalsis. The contractions are caused by stomach muscles trying to force food through the narrowed pylorus.
Dehydration. Your baby might cry without tears or become lethargic. You might find yourself changing fewer wet diapers or diapers that aren't as wet as you expect.
Changes in bowel movements. Since pyloric stenosis prevents food from reaching the intestines, babies with this condition might be constipated.
Weight problems. Pyloric stenosis can keep a baby from gaining weight, and sometimes can cause weight loss.
