My three week old has started doing a lot of stretching after he has nursed for a few minutes (really big stretches). It's not a problem except sometimes he turns his head violently while he's still latched on! Ouch. He spits up only occasionaly but last night he projectile-vomited. He does have a concerned look on his face sometimes and I'm worried that he might have GERD. Does anyone know what the stretching is about? Is it just gas or something?