Oxygen 98, possible lung scarring can anyone explain this to me please?

[Wiggins]

I kept myself well last year only being diagnosed as having very mild COPD and Asthma and I didn't have any chest infections or Colds. I kept excercising too. This Feb I had a spell in hospital due to an unrelated illness and came out with a chest infection (or not as the case may be). Anyhow I've taken four different courses of three different kinds antibiotic, the last being finished only last Wednesday. I'm still bringing light green phlegm up of a morning and then it turns normal but my cough is worse than it normally is. I also took a sample of my sputum to my GP three weeks ago. I had my COPD review last Friday and the nurse told me my stats had dropped slightly but I was still in the very mild bracket and I remember her saying my Oxygen was 98 and that was good. She then made me an appointment to see a doctor today.

I've seen him and he informed me all my stats were lower including my Oxygen levels and I'd lost 'some' lung capacity. He suggested that the stats show that I have scarring on my lungs. He also said that the results of my sputum test showed no pathogens. He then went on to say that my spirometry test shouldn't have been undertaken while I was coming off the back of an infection and it may be an erroneous result. The upshot is I'm to see if the phlegm clears and I get better and then arrange another spirometry test for July. I became very worried because he looked very grave. I can't remember the other stats but can anyone explain the 98 Oxygen level and the possible scenario of having scarred lungs.