Why do some people cough all the time for seemingly no reason?

^This. I have allergies and constantly get nasal drip and sinus infections all the time and sometimes bronchitis. Although I do go to the doctor each time (sometimes I have to go back 2 maybe 3 times after I finish each Rx of antibiotics for an additional refill). It's the most annoying thing, coughing all day to the point where I can't finish a sentence without hacking up a damn lung.