Shortness of Breath & Fatigue After Mild Exercise Only—Anyone Else?

Has anyone experienced similar symptoms? I’ve had Long COVID since April 2021. For the first few years, I dealt with severe fatigue and post-exertional malaise (PEM). While I’ve improved overall, any activity beyond walking still triggers PEM. About 24 hours after even mild exercise, I develop shortness of breath, followed by lung fatigue and general exhaustion that lasts for several days. I tried low-dose naltrexone (LDN), but it didn’t seem to help.

Has anyone found anything that helps with this?