My son caught a cold when he was 4 years old that completely locked his lungs down. We did the ambulance trip to the hospital as well as the x-rays, steroid shots, breathing treatments, and a nebulizer that was sent home with us. It was a scary time, and I couldn't imagine how he all of a sudden had asthma when he had never had it before. I started reading everything I could get my hands and about asthma and most of the books said the same thing, cut wheat, diary and processed foods out of the diet. This seemed impossible for me, and I didn't do this for a very long time. His asthma just progressed and got worse and worse. Back when my son had asthma, I came across a show on television called Know the Cause. The host of that show talked about candida causing asthma. After listening to him talk about how candida can become a problem for your body if you live in a moldy house, perhaps breathe in a large amount of mold from swinging hay, from breathing fungal or mold spores in dirt if you have been digging in it or perhaps working under a house, or in our case taking a lot of Antibiotics . My son has been on many prescription Antibiotics for ear infections which then turned into sinus infections with more prescriptions. Finally, we had a reason why he had gotten his asthma. He was on a vicious cycle getting more and more infections, with more and more Antibiotics . Our diet back then was conducive for fungal overgrowth, as we ate a lot of fast food, junk food and especially preserved processed food. I finally changed his diet to a lower carb-no grain diet with lots of veggies and some meats, and started him him on oregano oil, garlic, olive leaf extract, & grapefruit seed extract, plus quality vitamin/mineral and gave him probiotics at night before bedtime. We were able to completely rid him of his asthma and he hasn't had a problem with it in over 6 years now. Candida or mold (fungal) overgrowth might not be your problem, but it's worth looking into. I also read a couple of great books on the subject:
Allergy and Asthma Cure by Dr. Fred Pescatori
The Respiratory Solution by Cass Ingram
See if your library can get them in if they don't have them already. They are great reads on this subject.
http://www.knowthecause.com
you can watch his shows daily on his website. It has worked for my son. It's nice having a normal child now who can breathe when he gets a cold. He caught the flu last week and even with his cough, never once had a problem breathing or having breathing difficulties. Good luck in your search to get better.
Here's a couple of articles for you to read on:

Bronchial Asthma - Is The Allergic Theory Not Correct?
http://www.medicalnewstoday.com/articles/69238.php


Yeast Infection Causes Asthma?
http://www.articlesbase.com/alternative-medicine-articles/yeast-infection-cau...


Antibiotics Cause Asthma (Video)
http://www.bioportfolio.com/video/101-Pharmaceuticals+-+Antibiotics+Cause+Ast...


Baby antibiotics 'link to asthma'
http://news.bbc.co.uk/2/hi/health/4801118.stm


ANTIBIOTICS KILL YOUR BODY'S GOOD BACTERIA CAUSING DISEASE
http://www.worldwidehealthcenter.net/articles-264.html


Allergies and Asthma Can Be Caused by Systemic Yeast Infections or Other Fungi
http://www.yeastinfectionadvisor.com/allergiesandasthma.html