I'm experiencing persistent shortness of breath and this odd sensation like there's something stuck in my throat which makes me burp. I took a Covid test on June 17th, and it came back negative, so I'm wondering if it's possible for Covid not to show up on those tests? My Pulmonologist recommended an HRCT of my chest and an ECHO, both done by June 30th, and the results came back normal. I'm curious if an HRCT can sometimes miss Covid. Also, if someone has a heart blockage, would that show up as any kind of abnormality on an ECHO?