Sounds like oesophagitis to me, or even a hiatus hernia. The hernia can be caused by wearing trousers that are too tight: it happened to me in the 80s when I lost a lot of weight, had my pants taken in, and then went on a trip to Denmark and drank too much beer. The hernia happens when the stomach pushes up so hard against the diaphragm that the sphincter closing the oesophagus fails and a bit of stomach pokes up through to form a little pocket in the thorax. Gas or liquid can accumulate in this: you can feel it but not belch it away. It can also cause very sharp spasmodic pains that give a good imitation of a heart attack, as my doc joyously told me. If you drink anything fizzy the gas inflates the pocket and you desperately need to belch but can't.
One of the other consequences of this that since the sphincter fails to close completely, stomach acid can invade the oesophagus and give you heroic heartburn. The irritation also makes swallowing unpleasant. NSAIDs can make it worse because they reduce mucus production, and the interior of the oesophagus has a protective mucus coating that needs to be constantly renewed. You might need to avoid anti-inflammatories like Ibuprofen and Naproxen for a while. Medicines are available that depress stomach-acid production and help recovery. They can also counter the side-effects of NSAIDs, in fact it's common to prescribe the two together.
According to my doc, surgical procedures to alleviate the hernia are about 50% successful. Better live with it, he says. Fortunately, the intra-thoracic pocket can recede of its own accord and the symptoms disappear: however the weakness is there and overconstricting the midriff can bring it back PDQ.
In your place I'd return to the first doc and rearrange his fundament with my boot, because hiatus (aka hiatal) hernias afflict a hefty portion of the populace and you don't have to be old to have one. I was 39 when mine happened.