Not only was I damaging my lungs with smoking, I was asthmatic too. I must have been utterly crazy! When I stopped smoking, my chest got even worse. I put it down to clearing out the gunk, which is absolutely true.
But after six months I went to see my GP practice nurse, desperately worried my asthma was getting worse. She was fab and explained that there are tiny hair-like projections in the lungs called cilia. Usually they act as an air filter, protecting the lungs from dust, mucus, tar and smoke. Unfortunately cigarette smoke damages the cilia so they no longer work properly. You don't need me to tell you the damage that can be caused when a filter fails to work.
After stopping smoking, the cilia gradually start to grow back and function properly again. The initial downside is that breathing can sometimes feel more difficult. The nurse checked my lung function, assured me it had improved and said my awareness of my breathing was perfectly normal as that is how your lungs are supposed to work!
After that I set about staying off cigarettes and getting more exercise.
Now, three years on, I have more stamina and lung capacity than I had at 25. On top of that, I now know that my lungs are functioning properly and mopping up all the nasty stuff we all inhale every day (fumes from traffic jams, the smoke from smokers clogging up the doorways of pubs etc!).
So, if it is taking longer than you expected to get your breathing back to normal - be patient! It's just your body starting to work the way it was designed to again!