I have this too. It’s acid reflux. It happens even if no acid actually comes up. I went to an ENT. There’s a valve that loses tone after years of this happening and it allows acid to creep up the esophagus and causes gagging especially if you’ve been coughing. Stress also makes it worse for me. I was on Prilosec for a bit, but I don’t want to be on any medication while pregnant.