Sometimes babies swallow excess air because they have a tongue and/or upper-lip tie which prevents them from getting a good latch.  If the baby makes clicking sounds while nursing, that means the seal is being broken and air is getting into its mouth.  Having these tight frenums released is called a frenectomy.  Frenectomies done using a laser are safe, heal quickly and do not involve hospital visit or general anesthesia or stitches.  There is a lot of information about tongue ties on the internet.  Sometimes is it not an allergy but rather just a mechanical problem that can be quickly and safely addressed.
Leslie Haller, DMD of tonguetiesouthflorida.com