I would not be suprised if you have some asthma. Asthma often presents as a dry cough which is often worse at night. There is a strong association between asthma a sinusitis.
http://www.aafp.org/afp/20031015/tips/16.html
Infection anywhere in the respiratory tract - including the sinsuses can aggravate the asthma symptoms by triggering bronchospasm. For information on asthma check out this link:
http://www.aafa.org/
I have had good results with treating patients with your symptoms with 2-4 weeks of inhaled corticosteroids and/or bronchodialator (Pulmicort and Proventil are examples of each, and Advair is a inhaler that contains both classes of medication)
The other thing your physician may want to consider is the use of a nasal steroid such as Flonase which may reduce some of your symptoms
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