Mr. and Mrs. Flint bring in their 6 week old baby boy, Charlie, to the Emergency Department (ED) You are completing a shift in the ED as part of your pediatric clerkship rotation.  The parents tell you that Charlie has been vomiting after feeding for the past week. While gathering a history, you ascertain that the vomit is not green and non- bloody.

What is your differential diagnosis for non bilious and non bloody vomiting in an infant?