What Causes Dry Cough In An Infant?

Hi i have an 8 month old daughter shes had a really bad cough now for about 2 weeks iv been to my doctor she prescrived linctus said it was dry cough even tho shes throwing up flem i can hear her chest like flemmy , wen she had her first 2.5 ml of linctus she went noticably worse where i took her to hospital because she kept goin blue and they still said it was nothing what could her cough be and does linctus have side affects