I can relate to your experience, both with air trapped in my stomach or esophagus, as well as heartburn. I've experienced both. I think it is somewhat normal to swallow a fair amount of air while either smoking analogs, or vaping. Having said that however, I do not think it is totally normal for someone with no health issues, to suffer either of these conditions in an ongoing manner. What you may want to consider doing, is see your doctor and have him or her check you out for GERD, otherwise known as Acid Reflux Disease. It is fairly well documented and something that you can readily google and investigate, that nicotine has has sort of a "relaxing" effect on the "valve" between the top of your stomach and the bottom of your esophagus, called the LES (or lower esophagal sphincter). This "valve" is supposed to function only as a one-way valve, allowing food and liquid into the stomach from the esophagus, but not allowing any stomach acids or substances back up into the esophagus. For people who have varying degrees of GERD (or acid reflux disease) sometimes also accompanied by a hiatal hernia (a condition where a portion of the upper stomach protrudes up through the abdominal diaphragm thereby distorting the LES somewhat), the nicotine in both analogs and vaping, can relax the LES enough so that it no longer functions in only one direction. This allows stomach acids or other substances back up into the esophagus, causing several possible symptoms, including heartburn, outright pain that is sometimes confused as heart attack symptoms, excess gas and burping, and also the feeling you described of needing to burp but cannot.
I have been diagnosed with GERD for over 20 years now, and have experienced all of the above symptoms at one time or another. I suffered quite a lot in the beginning, until such time it was actually diagnosed in me as GERD. Prior to that time, I lived on Tums or alka seltzer, or other self remedies. After a couple or three years of that, I was finally diagnosed and began treatment. Treatment consists of only one long acting capsule per day each morning (in my case, Prilosec). At certain times when my GERD is acting up more than normal, a second capsule is sometimes needed later in the afternoon before my evening meal. These medications work by merely cutting down on the amount of acid your stomach produces.
Additionally, I have to be very careful with the level of nicotine I vape. Although I was a heavy smoker (2 PAD plus) I smoked ultra lights and had gotten to the point I barely inhaled. So I don't really need a lot of nicotine in vaping and am able to vape 6mg or less without too much problem, typically. Some days however, even the 6mg bothers me and I have to cut down on vaping, or go to 0mg liquid which I keep around just in case.
Just as kind of a test, try cutting down on the nicotine level in your ejuice and see what if any effect that has on your problems. Keep in mind when you do this, that if you do have GERD or some other digestive problem, it is not constant. What I mean by this is, that day to day, your body changes as will the GERD (if you end up having it). Therefore there will be days that one level of nicotine will be fine and cause you no apparent problems, but then the very next day it will cause a problem. In other words, like all bodily events, they are dynamic as opposed to static. You've most likely already noticed this dynamic state, simply from foods you eat that one time seem to be fine, but the next time cause you a problem. Same thing.
GERD is not a big deal necessarily. But it definately IS something that you want to treat if you do end up having it, as failure to do so will cause ongoing and uncomfortable symptoms, as well as scarring of your esophagus, which can become a serious issue.
