I'd say 99,9 % of the time it is just a natural side effect of coughing / the inflammation of a cold or flu virus.
PS: If it IS a cold, antibiotics won't do anything,as they kill bacteria, not viruses. (And incorrect use is the reason for so many resistant bacteria appearing in our days)
Try to find a more efficient cough medicine? I find that Cosylan helps (dunno if it is called that over there), it contains Ethylmorphine, so beware if you need to operate heavy machinery