I'm obsessed, I'm also worried about lung issues (among many other things)! I know it's hard to do, but please calm down! Do you know what causes shortness of breath, a lack of oxygen in the system, and failes spirometry tests? Anxiety! In high school (this was over 9 years ago) I took a spirometry test as part of a study a group was doing on high school kids. I'm a non-smoker, and I used to jog quite a bit every day after school and participate in many intramural sports. I was really nervous because it was a 'test' and I got a 'severe pulomonary obstruction' type reading because I wasn't breathing properly due to nerves. The nurses who were doing the test even told me it was from anxiety but I freaked out anyway. I went to my doctor, and sure enough, I did not have any pulomonary issues. Being out of breath can be a combination of being anxious and out of shape. It's also possible that you're paying much more attention to your breathing now.
You're doing all of the right things, and you're getting all of the right tests. Your doctor says you're fine so I really wouldn't worry about it! Apparently we all lose some of our lung capacity after a certain age, too. If you're taking the spiro test again and again with different results within seconds, I'd say it's anxiety. My fingernails are also pale and there are many causes for that. Right now I have a thyroid condition and I'm very slightly anemic so my circulation and blood oxygen is probably not the best. Try to relax and do something you enjoy to take your mind off of this. Keep going to the doctor, and continue exercising and know that you're not the only person with a bad spiro reading and no lung conditions!