have you been allergy tested? is it possible your house may have mold? do you have animals? what about dust? do you do the yardwork or filter your house air ducts? do you live in a high-pollen area?
you also may want to watch what you've been eating. if you get heartburn, reflux can cause asthma-like symptoms. if you have been eating foods that you could be allergic to, this can cause asthma too. and you can be sensitive to cleaning products/chemicals in the house or vacuum, down pillows and comforters, etc.
i get asthma-like symptoms all the time. i also have horrible allergies to everything and reflux to the combination makes me very short of breath. my mom's asthma, which is severe, got worse when she ate walnuts and peanuts. she was tested and found she was allergic to them and other vegetables. if you have asthma, you likely have allergies, and if you can have allergies to pollens you can have them to foods and other things. you can also develop new allergies.
oh, and be sure to stay away from cigarette smoke!