Hello and Welcome to ‘Ask A Doctor’ service.
I have reviewed your query and here is my advice.
You haven't specified the duration of this symptom, which is very important in order to form a proper differential diagnosis. I can make some suggestions though. First of all, sinusitis
may indeed cause cough and phlegm. Sinusitis may even cause chronic cough
. In most cases the diagnosis is made clinically (with medical history and clinical examination). An X-ray of the sinuses
will help. "Full" sinuses do not always mean sinusitis but clear sinuses safely excludes this diagnosis. If your cough and the rest of the symptoms are recent in onset then a bronchitis
is a potential diagnosis. Bronchitis cause cough with phlegm and usually lasts for 2-3 weeks (or even more). The X-rays are negative in bronchitis. If your symptoms started more than a month ago then other disorders might have to be considered. In that cases please post a new question with more information about your symptoms and what you've tried so far.
Hope I have answered your query. Let me know if I can assist you further.
Dr. Panagiotis Zografakis