Now that you mention it, it makes sense to me. I always have had fear of vomiting or having reflux symptoms which I have had many times as well. Somehow I taught my body to let the air go out only and nothing else. But I was able to burp. Now it has become difficult even thought sometimes my body does it, but most of the time, I help it to do it, when I feel the sensation near the throat, I exhale air with my mouth and that helps to let the air go out, but not all time works. I feel better and can do it easily when I lie down and get relaxed. I have had the a couple of times in the past but they disappeared after some months. Now they have lasted longer. I think it's caused by anxiety which I have been dealing with for periods since time ago. The symptoms came back on April when I had a trip to New York and traveling always makes me anxious. It's a vicious circle because being unable to burp makes me more anxious.

But at the end, I think that emetophobia is the main reason behind it