Why do babies spit/vomite. i have a month old and just wondered is it becuaes of being full?

Reflux: Reflux by itself is with us thru out life. If you can burp/belch/spit up then you reflux. Reflux disease implies important negatives:pain, weight loss, etc. Reflux without pain is normal and common in babies.Upright posture after meals helps most of us avoid it. As long as babies feed often and lay flat, gravity is not helping keep the food down & they may have it.