That spot is nicknamed "gas alley" by doctors. It could be just eating more than usual, trapped gas, stomach pressing on diaphragm area and/or irritated nerves in that area. I had a similar problem (for years) and it turned out to be an irritated dorsal scapular nerve. A physical therapist demonstrated some movement exercises for the mid back and also glide movements for the DSN and I no longer have a problem. One very simple thing he told me to try was just lift my left arm straight up close to my head and lift the rib cage a few times. Doesn't have to be strenuous, just a gentle motion. Do that several times per day. This helped me a lot.