There are several different possible causes for a chronic cough and I recommend that you speak with a pulmonologist
. My first question for you would be whether or not you are a smoker. Smoking is one of the most common causes of chronic cough. If you're not a smoker, but work in a condition where you are inhaling some type of toxin often, this could also be a cause of a chronic cough. Exposure to cigarette smoke for a long time even if you quit at some point, could result in the condition chronic bronchitis
which also causes a chronic cough. If you have high blood pressure
and are taking the medication lisinopril, ramipril, captopril, or another medication that ends in pril, this could also be a cause of your cough. A cough that is worse with lying flat could be due to acid reflux. If drinking fluids such as ice water sets the cough off, they could be that you are aspirating small amounts of fluid when you swallow which can irritate the lungs and cause a cough. I think that since you have had your cough for so long, you should start by scheduling an appointment with a pulmonologist. This is the type of physician that specializes in this type of problem and will know what diagnostic testing you need first.