How Can severe Chronic Cough Be Treated?

Hello, My 7 years old daughter is suffering with prolonged acute cough and we are worried whether pertussis could be the cause. She has a very troublesome cough that is hard distinguish whether it is dry or wet, although she says that she sometimes coughs up small parts of sputum. It is difficult to recognise when has the cough really start since she suffers with some allergies which makes her nose runny and make her cough (these manifestations come and go). These uncertain cold/allergy cough has started a month ago. Two weeks ago suddenly she has got a mild fever lasting for two days and very little of runny nose (clear thin discharge) slight irritation in throat which lasted only for a day. Then the bad cough has started.. exhausting coughing spells that hardly allowed to breath, talk, sleep.. On the third day we took her to the doctor who prescribed he clarithromycin. After 2-3 days of the treatment of her cough has seemed to be resolving, but another two days later it has started to increase rapidly. Now she has completed her 7 days of antibiotics and her cough is very unsettling and worsening. She doesnt have a whooping cough, but except of the whoop, the severity and the type of coughing seems very similar to pertussis. She keeps coughing until she vomits and is very restless. What could it be since it stopped responding to clarithromycin half way through the treatment? I myself have a bad chest infection and am on clarithromycin 500mg for 10days, but my problem seems to be quickly resolving. My young son (4) has just started coughing lightly today too. Many thanks for advice.