your baby is gagging because he does not know how to manage his mucous drainage. the can't blow his nose or hock a loogie at this point. since he is a boy i am sure he will develop this fine art as he ages. right now you are really doing all that you can: suck out his nose use the saline nasal spray and the humidifier. remember that the purpose of gagging is really the body's attempt to clear the airway and that is really good.
what can do when 4 month old gagging on mucus. . doctor says he is fine because there is no infection. we already use vaporizer saline drops & mucus bulb