Hi,
I have nearly identical problem as jfoster23 mentioned. I am male 30, health and fit. But this pain/pressure start building up on my chest, a bit to the left / under breastbone. It has been 2.5 months now. I have also developed very tight tendons and muscles at the mid back, which make me struggle to site in the office.
I have done ECG, Stress test, Blood work, X ray (twice), CT, Gastroscopy... not thing the doctors could spot... Was diagnosed with reflux then costochondritis... but they just don't fit the picture.
I am considering to get help with Tranditional Chinese medicine now. But the uncomfortableness really make me stressed.
Did you get to the bottom of this, jfoster23?