Re: Vomiting after and between feeds
4.5 months old, not 4.5 years old, right?
Spitting up is normal for babies. It's probably not anything you're doing or not doing or eating or not eating. It's just that in young babies, the muscle sphincters which keep tummy contents down where they belong are, like all of a baby's other muscles, relatively weak. Even if your baby wasn't a big spitter before, it's not too surprising that he has become one now: at 4.5 months he's probably a lot more mobile than he was a couple months ago, and as babies start to squirm in new and exciting ways and jostle their digestive system around, spit-up frequency can increase.
I wouldn't suspect reflux unless he is always fussy, showing evidence of discomfort (e.g. back arching, crying in pain), having other reflux symptoms (e.g. bad breath, poor weight gain). But it wouldn't hurt to bring the possibility up with the doctor.
This could also be a tummy bug. If it the spitting up suddenly stops, or you see some diarrhea, a viral or bacterial infection would be a good explanation for what you're seeing.
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