Gag reflex. Everyone's gag reflex is different. It is possible to gradually overcome it, for example, sword swallowers at the circus.
Look at patterns. The gag reflex is normal and is designed to protect our airways from aspiration of food or stomach contents which can be harmful to the lungs. Some people have more sensitive gag reflexes and have difficulty even brushing their teeth. If this is a change for you, i would have concerns about whats going on the the mouth and throat and want this to be evaluated by an ENT specialist.