@gabrielm Were you tested for h-pylori? I had the exact same breathing problem for years! Had low hemocrit for years, elevated A1C levels to the level of being diabetic and couldn't climb a flight of stairs without being out of breath. Had an endoscopy with biopsies. H-pylori treated with high dose antibiotics. Breathing issues resolved. Low hematocrit resolved and A1C returned to better than normal.
H-pylori blocks your body from absorbing red blood cells and other nutrients. So, once the h-pylori was treated, the body is able to absorb the red blood cells which then allows more oxygen in your system and my breathing issue resolved. I hope your issue is that simple too. Just took 20 years to figure out.