What Is The Treatment For Persistent Cough?

hi doctor, i have an extremely bad cough..it usually occurs around 3-4am and lasts until im fully awake and during the day i am completely fine. its a chronic cough, sometimes its dry and sometimes i vomit phlegm. cough syrups, lozenges and anti-allergy pills haven't helped at all.. should i be worried? what do i have and is there a cure?