K.P.
Sometimes respiratory ailments can be caused or worsened by allergens -- whether in food or your environment. Some people get bad allergies because of dust mites, animal dander, and other stuff that stays in carpet and carpet padding. Many people have gotten relief from removing carpeting and moving to all hard-surface floors (tile, wood floors). You may want to consider this.
Some people also are sensitive to dairy products. My SIL's kids are constantly sick, and end up in the hospital or having to go to the emergency room with breathing difficulties at least a few times every year. I honestly think that they are sensitive to milk, which she makes them drink every day (for calcium, and because it's "healthy," y'know).