Guys, for a lot of you not all. This is anxiety. I know you have heard this countless times, and youll respond but im not anxious or stressed. However anxiety doesnt have to be mental. You can get a very distressing physical sensation and that will then cause you to fear the sensation and it comes back and back over and over again. However the way to live better with this is not by thinking your way through it with talk therapy or cbt. It is total acceptance of the sensation. It may surprise you but i will say you have totally accepted before, when the breathing sensation has been gone for perhaps a few hours or even days. However in its place was another 'issue' waiting for you to solve. I see the owner of this chat complains about sinus issues, i had similar issues i was considering nasal surgery. But not because i had a genuine issue it was all the adrenaline and cortisol built up from this breathing senastion i feared that caused me to hyper-fixate on a problem to fix. This is called somatic shifting in anxiety world, some of you may have gastrointestinal issues or pain or mental while you are free from the breathing one.
So, the solution is simple, yet the hardest thing to do speaking from personal experience. Total acceptance. This means not trying to feel better by avoiding distracting or thinking your way through it. If you feel bad you feel bad go about your day. (Id like to thank the person on this form who said breathing ocd cause in a way it is, it is all of you guys trying to DO something about the feeling is whats keeping it there). Acceptance means not letting it affect any part of your life, work as if you felt nothing, go out as if you felt nothing. Due to your poor habits you have caused this feeling to stay for aslong as it has. I suffered as much as all of you, everyone can recover.
READ ASAP
Hope and Help for Your Nerves
Book by Claire Weekes
At Last a Life: Anxiety and Panic Free
Book by Paul David

Also any anxiety teacher who reps these kinds of teachings,
I like shaan kassam but books first.

Understand there is nothing to fear anymore your breathing issues is just adrenaline making you feel breathless or suffocated or laboured breathing. Acceptance is not a tool though, cant go oh i accept when you feel bad and wish it gone asap. Acceptance is living your life with and without the sensations and DOING NOTHING TO FIX IT, let your body and brain heal itself. The books will explain all your questions.

Please if you are struggling just give this a chance, stop making all these medical appointments, these supplements or breathing exercises.
STOP TRYONG TO FIX THIS, LIVE YOUR LIFE AND ACCEPT IT ALONG FOR THE RIDE WITH NO FEAR OF IT. AND EVENTUALLY LONG TERM IT LESSENS TO THE POINT IT GOES FOREVER.