Good heavens, I could have written this myself a few weeks ago. I had what sounds just the same pain behind my right shoulder blade. It hurt when I breathed deeply, moved, coughed or when I walked and was breathing more heavily. I did feel slightly breathless but maybe because it was hurting I was breathing more shallowly. I had also had slightly prickly eyes and a scratchy throat before this, as if I was coming down with something, but it didn’t turn into anything. I have had pleurisy before, and thought that’s what it probably was. I did end up consulting 111 website when it didn’t go away, and settled under my arm/ribs on one side and niggled on the other. After answering loads of questions, 111 told me to phone 999! So I backtracked and changed a couple of answers to questions that didn’t really ‘fit’. Then it said call GP. Long story short, phone consultation suggested either pleurisy or costochondritis. Unlikely to be COVID 19 related. Dr Google said costochondritis is in completely different part of chest. It has virtually gone now. I hope that helps, and you feel better soon. If you don’t, 111 or GP. ?