If the drs are clueless and concerned, we won't have many more answers, panic attack sticks out though, as I have anxiety and have had pains I can't explain,dr tells me it's cause of that and also online says it's a symptom, not sure how the pain is for you with your chest. I've had pains, I wouldn't say was my heart, but it wasn't surface, so I assume my lungs. Pregnancy can make anxiety worse. Mine subsided. As for stomach pains directly across from your belly button, high or low? Maybe webmd.com can help you more. They have a symptom checker.
I can't personally say I've gone through this, but hopefully others who have will be able to post and tell you their experiences. I hope you can figure out what's going on and get some answers.