How long after bronchitis does the cough last ? it's dry and annoying and constant and nothing helps

It varies: Duration of cough in bronchitis depends upon factors such as concomitant infection, allergies, asthma and sinus involvement etc. Proper Evaluation and adherence to recommended treatment to medicine, including avoidance to allergens would assure a shorter course of bronchitis/cough. Feel better:)

Bronchiolitis: Sometimes after Bronchitis, there is a residual irritation of the airways called Bronchiolitis. It is important to see your doctor as they can do a quick and easy test called a Peak Flow Meter which will rule out Asthma that can sometimes happen after Bronchitis as well. Moreover your doctor maybe able to prescribe something to make you feel better.

Post-tussive cough.: When we're sick with an upper or lower respiratory infection, the cough tends to be the last symptom to clear. This is called a post-tussive cough which, as you can surmise, means "post-cough cough". The coughing itself makes the cough linger. The solution? Cough suppressant. This cough, left untreated or unsurpassed, can last several weeks.