How Do I Get Rid of This Mucous and Cough?

Question

I am at 62 and I am suffering from asthma badly. I am using a combination of medicines which include Advair , Atrovent and singulair. I am living upon these medicines. My problem is expectoration of mucus which is mainly yellowish in color from the bronchial tubes. This is happening in all my waking hours and most of the time, I have this problem. I try to cough to get rid of this mucus. I also noticed its color changes into yellow in the morning and white in the rest hours. I cough more than 20 minutes continuously before going to sleep. This is my every day practice. I saw many doctors and nothing seemed effective for me. I need some suggestions or advice from people who have the same disease.