I remember before finding out about my asthma I use to run everday(3 years) and then started having small episodes of shortness of breath(with wheezing) but didnt think anything of it. about a year later it got worse but I was able to still run and sleep well, year after that I went into full blown asthma and after 3 years? it is now severe and Im unable to run due to very bad shortness of breath enough to wind myself into the hospital. I still do some light weight lifting to stay in shape but I miss running. One more thing I have good peak flow readings and still have wheezing with shortness of breath might want to get your self checked out and not count so much on peak flow measurements alone. Good luck:)
Pulmonary fibrosis would have those symptoms, though I don't know if you could run with that condition. It could be stress or anxiety. Try to think about things that were going on in your life before this started. Major changes, losses, relationship issues, etc. If something with a big emotional charge came before the symptoms, then I would consider it. Also watch your thoughts. Have they become more fearful or negative? Go in and have a pulmonary function test done and a chest x-ray. Talk to your doctor.