Hi @whoami, thank you for sharing your situation. I hope you know through this forum that you're definitely not alone!

And thank you for providing this information. I'm glad you went through some tests to start eliminating things that could be causing it. You mention about slight improvements when you use an inhaler. Your lung function test came back normal, though I'm not sure if it would catch the possibility of occasional or sports-induced asthma. That could possibly explain the improvement when using an inhaler.

Have you tried reducing the intensity if your running for a time, just to see how that might affect your breathing overall? I definitely had to play around with the intensity of my own exercise until I found a "sweet spot" where I wasn't pushing my breathing too hard, but it was meaningful exercise.

Also, have you done or considered getting a sleep study done?

By the way, I too had mild anemia in my bloodwork back over a decade ago, which I think has since resolved, but at that time I seemed to be lacking in some nutrients. I'm not sure if that played a part in breathing symptoms, but I am speculating that lacking certain nutrients can affect the ability of the body to transport oxygen regularly.