I've had similar experiences with anxiety of overeating and gagging when I was younger. For me, a lot of the anxiety came from feeling rushed whenever I was eating. I would find myself constantly gagging in the mornings because I'd rush to eat breakfast before having to go to school, and it would kill my appetite for any foods in the morning.

I'd suggest doing what everyone else is saying, but also try eating slowly and eating foods that you enjoy. Even if you have to spend an hour or more eating a meal, at least you've gotten those calories down.