I'm dealing with some breathing issues over the last couple of months. I've tried ECG and echo tests, and I've been taking gastritis tablets every day. My oxygen levels seem fine, like 99 on the oximeter, but the doctors keep saying it's nothing. But I constantly feel like I'm struggling to breathe, like air isn't coming in right through my nose, and there's this pressure in my chest making it hard to breathe properly. Can you help me figure out what's going on?