How to avoid production of Phlegm in the body?

When I go to bed at 11 pm,, I get good sleep for just 4 hours, and a sudden cough wakes me up. After two or three coughs, phlegm comes to my mouth along with cough. Since I do not like to swallow it, I will be forced to get up and go to bath room to spit it out. There, for 5 minutes, cough with phlegm, spitting it out, continues 4 or 5 times. That is all. Afterwards I can go to sleep for another 4 hours, without any problem. This is a nuisance to my wife and is annoying me also. Please tell me how to avoid formation of phlegm itself in the body. or atleast, if it can not be avoided, how to make it dry out within the body itself, without it coming to my mouth?