There are a few possible reasons for your persistent cough. First if you are a smoker or are exposed to 2nd hand smoke this is a common reason for a persistent cough. Quitting in this case would be the solution. If smoke is not a factor then you have to rule out the possibility of heart medications causing the cough as a side effect. ACE inhibitors used for blood pressure commonly cause a persistent dry cough. If you are not on heart medications then consider post nasal drip. This can happen after a cold or from exposure to allergens (either food or environmental). If you haven't been tested for allergies then consider seeing an allergist to find out your personal allergies! If you've already done this then consider doing an IgG food sensitivity test or an elimination diet with the guidance of a naturopathic doctor to rule out food sensitivities that may be triggering your cough. In the mean time consider using the "neti-pot" to irrigate your sinuses and reduce post nasal drip. Also consider using an herbal demulcent "Marshmallow"....not the candy from halloween but the medicinal root whose latin name is Althea Officinalis. Apparently it's comparable to codeine in it's cough suppressing effects but without side-effects. Marshmallow, slippery elm and licorice root have all been shown to be effective for dry, hacking coughs.

For more information on Marshmallow see the following link:

http://www.wyldeabouthealth.com/healthnotes/us/assets/nutritional-supplement/marshmallow/