Any ones child have a cough that lasted almost the whole year on and off? What is it?or what helped

Drs have tried antibiotics, I’ve tried nebulizer, allergy medicine, cough medicines and nothing. My daughter is 4 and I need to help her I don’t know what else to do. Sometimes it’s realllly mucusy and sometimes dry. She coughs a lot at night I also tried the cool mist humidifier