A couple of months ago I was eating lunch and had to burp. I noticed that as the gas was building I felt an aching pain in the left side of my middle back area. It has continued since then. I sometimes have the sensation as I can feel something moving down my esophagus, but it's mostly as gas is building toward a burp. It doesn't happen every time I burp, but does happen on a daily basis. I've always had a lot of gas, so the amount is nothing new. On occasion I will feel a bit of discomfort under my left breast, but those occasions are few and far between. I don't have any other issues - no nausea, vomiting, diarrhea.
I will add that after this started I did develop issues with my back - pinched nerve in right shoulder blade with pain in my right arm, left side neck stiffness and pain - and I'm usually tense in my neck and shoulder area. Don't know if this is related, but thought I should mention it.