It is not uncommon to have cough for complex (several combined reasons) reasons...meaning that it is not due just to one single cause. "In several studies of patients with chronic cough who were referred to pulmonologists: postnasal drip, asthma and/or GERD were found to be the cause of cough in 99 percent of immunocompetent nonsmokers who were not taking an ACE inhibitor (or beta blocker)...high blood pressure & cardiac drugs...and who had a normal or stable, near-normal chest radiograph. The methacholine inhalation challenge test (for asthma) was the most helpful test in making a diagnosis of asthma if the history was not suggestive. In 57 percent of patients diagnosed with asthma, the positive methacholine inhalation challenge was the only test indicative of the disease. In 23 percent of patients diagnosed with GERD, the prolonged esophageal pH monitoring test was the only indication of the disease. GERD is a recently recognized cause of chronic cough and is identified as the etiology of cough more frequently in studies that use prolonged esophageal pH monitoring as part of their diagnostic work-up. Sputum cytology may help if eosinophiles are identified (may indicate asthma or others, see chart below); lipid laden macrophages tend to reflect pulmonary aspiration of GERD material.

"In children, cough-variant asthma is the most common cause of chronic cough. However, in children younger than 18 months of age, congenital etiologies are an important cause. Chronic cough frequently has multiple causes. The authors of the studies cited in Table 1 found a single cause for cough in only 41 to 73 percent of patients, two causes in 23 to 42 percent of patients and three causes in 3 to 17 percent of patients (it is a "complicated" cough when more than one cause at same time). Many patients were correctly diagnosed by their primary physicians before being referred to a pulmonary specialist but had not been treated aggressively enough to stop the cough. The family physician is capable of directing the work-up, making the diagnosis and treating chronic cough in an estimated 90 percent of cases of chronic cough.¹" Cough causes can be mixed and not just a single cause, see above.

As a patient, you know what your habits are; but you may need to check your medications to see if any of them cause a chronic cough. There are two types of cough, (1) dry (non-productive) cough and (2) productive (sputum is produced) cough. A productive cough is more likely due to asthma, chronic irritant or allergic bronchitis, aspiration of gastric juices into the airways (post-stroke or GERD), and infections. Non-productive cough is more likely related to medications and non-lung causes. But some of the potentially fatal infectious "atypical pnuemonias" can be non-productive. Fever is a typical indicator of  infectious causes of cough...but "low grade" infections may not cause obvious fever. "Dry weather" or winter cough in normally moist geographic areas can complicate colds and other cough causes.

Some insight can be gained medically by looking at sputum coughed up from the lung (not snorted or coughed from the back of the throat or nose and not "spit" or saliva). Noticeable amounts of actual sputum are most likely available just after getting up from a night's sleep. Coughing the sputum into a white lavatory sink allows one to note slight color differences that are important. And, that same sputum can be used for bacterial or fungal cultures or for microscopic exam by smear or cell block. Put it into a cup or container and take to your doctor or the lab.

Acute bronchitis is when the process lasts 3 weeks or less. True chronic bronchitis is a cough that lasts at least 3 months per year for at least 2 consecutive years; and when more frequent or sustained, it is called ACEB (acute exacerbation of chronic bronchitis) and often in those with COPD (chronic obstructive pulmonary disease).

References:

1. An Office Approach to the Diagnosis of Chronic Cough, W. Ross Lawler
   American Family Physician, Dec. 1998.By way of search engine in "Find Articles".
2. Chronic Cough, ELIZABETH B. PHILP, M.B., CH.B., University of Alabama School of Medicine, Tuscaloosa, Alabama, American Family Physician, Oct.1, 1997.
3. Lipsky M, Le J, Therapeutic Management of Bronchitis, Preventive Medicine ion Managed Care 5(1 sup):1-8, February 2005.