I just found your question here as I normally help moderate the cardiology topic.
It is entirely possible that an inept nerve block caused the intial pneumothorax, although you also could be one of those people born with a certain number of "blebs" on your lungs, which occasionally will break and sometimes cause a partial collapse of a lung. Since your first pneumothorax happened subsequent to a medical procedure involving a needle insertion, however, it is just as likely to have been a medical error. In either case what you've experienced since has very likely been related to it.
Your echo results actually yielded nothing of importance (a very high percentage of the healthy population has minor regurgitation in one or more heart valves). I don't think your problem is "all in your head." What it is isn't clear, especially at a distance, but given the pneumo history, I wouldn't blow off your current complaint. From your description of the pilates-related symptom, I think you were feeling crepitus related to a second, probably very minor breach in the lung where the first pneumothorax occurred. It apparently wasn't as significant, and probably resolved on its own. You may have been experiencing trapped air in the pleural space since the first event, and that could have accounted for the other symptoms. There is, after such an experience, a certain psychological component that enters into the equation ("waiting for the other shoe to drop"), but ths is reasonable when the symptoms have not altogether subsided, and I don't think it is causing your symptoms, although as increasing concern turns into anxiety it makes it more difficult to recognize concrete symptoms from the usual funny business the body pulls on a day-to-day basis. Had your doctors been more thorough to start with, you probably wouldn't be feeling this way now. Rather than acknowlege you could be having sequelae to the initial pneumothorax, they are trying to marginalized it. Unfortunately this leaves the patient feeling marginalized (and rightly so). The patient is actually who is being treated. The problem isn't just a symptom, not just a body part, but a person. Sometimes this fact is forgotten in the business.
Pllates actually is a great no-impact exercise, but because it involves stretching it definitely could have caused an aggravation of the original site. Hopefully it's no worse than it was, and small pnuemos are sometimes allowed to heal on their own, but if symptoms persist I would think someone would at least take a look to be certain there isn't some air trapped in there. Since air doesn't show up on x-ray (although a collapsed lung usually will), there can be pressure between the pleura and the lung just sufficient to make a person feel very uncomfortable (cause some symptoms) without being obvious on a cursory examination.
If you can't get a better answer from one of your doctors, perhaps you could get a referral to a pulmonologist or at least insist on a second opinion. Everyone's entitled to one of those.
I hope by now this has resolved on its own. If not, please do follow up with us. Good luck to you.
John Kenyon, EMT, CCT
Non-invasive cardiology tech, Emergency and Critical Care technician, Critical Incident Stress Mgmt. specialist