I have experienced chest pain that came from my stomach (I had GERD for years), sometimes severe enough to double me over in pain. I've also had chest pain from pleurisy, but you'd feel that more than just when exercising. In your position I would hold off on running and such until you get a green light from your doc, and perhaps some idea of what it is if it's not your heart. I know you've lost weight and reduced your cardiac risk, but sometimes things pop up after you lose weight. I lost 40 lbs and then all of a sudden developed knee problems, which ticked me off and felt unfair, but there you go. Hopefully this is just your stomach or esophagus- maybe a spasm in the esophagus? But I'd definitely hold off on the hard stuff until the doc's run his tests.
"A mistake is not failure but feedback. -Rod Gilbert"