Constant Coughing, and feel weak

Hi I am 60 years old, and in these past 2 weeks I feel weak, powerless and started coughing.  I have been taking cold medicine but they don't seem to work.  I don't feel any chest pain, but this constant coughing has cause me sleepless nights.  And I have went to the doctors but they can seems to find an answer.   Hope someone  can give me an advice.  Is this a sympton of any types of cancer? maybe lung cancer since I am 60 years old.  Any advices are appreaciated.

[National Jewish Health]

Being weak and powerless can be signs of a systemic disease or simply result from sleep deprivation.  The presence or absence of other symptoms, for example loss of appetite, weight loss or myalgias could provide additional clues.  A cough of 2 weeks duration could truly be on the basis of a respiratory infection, believe it or not, including pertussis, commonly called whooping cough, or on the basis of a respiratory infection.  And, yes, cough can be a sign of cancer.  If not already performed, you should have a chest x-ray and, if that is clear or normal other causes of cough, including postnasal drip and gastroesophageal reflux disease (GERD), commonly called acid reflux, should be considered.  Your doctor should try to determine the source of your cough, be it upper respiratory or lower respiratory, and investigate further, accordingly, with blood counts, sputum cultures, sputum cytology and, if no clues are forthcoming, consider consultation with a lung specialist and/or an ENT specialist.