Lungs and coughing. Nicotine from lungs.

During my college days i used to smoke about 5-6 cigarettes a day but for past 3-4 years I smoke 1 or max 2 cigarettes in a day and its more on the day i drink (once in 15 days). I have unusual Dry cough specially during night its like irritating and itching in my throat for an hour. It not that much cough but around 20 times i cough during night. During day time i do not have this problem. Time of smoking 1 cigarette everyday is around 6pm after office. After reaching home i dont smoke and i always have healthy diet with milk and all. I also eat fruits everyday. Please tell me what is this problem and what best i can  do to make my lungs healthy forever and Which is the best fruit to clean out nicotine from lungs. Thanks Doctor! .