Hi gabi,
have you ever considered that you may be having mild panic attacks/anxiety? I used to discount this theory completely for myself until one day after major surgery, I made a trip to er and there was nothing wrong with me. I am managing now with a program (pilates) to increase my flexibility and strengthen my lungs. I am also beginning a workout program with weights and swimming to combat my stress. Asthma worsens for most of us when we're stressed out. Many aspects of asthma remain a mystery, but being true to yourself by exploring every possibility and quitting smoking should greatly improve your health. I used to smoke and quitting was the best thing I ever did. My lungs are actually more sensitive now, but that is a sign that they are alive and working to clear foreign particles away. I am beginning singulair today and i'll let you know how it works. It is for allergies and asthma because they are so intimately connected. However, you may not realize a big difference if your asthma is purely stress or exercise induced.
Explore your options, keep an open mind, and most importantly, have a good honest talk with a health care professional. Like I said, I ignored my anxiety thinking I had a heart problem in the beginning and I don't. I am completely healthy with the exception of my allergies/asthma.
I wish you well my dear.