Hi, Had it been lung infection, you would also have had other symptoms like fever and malaise. If you only have been coughing without any other problems, then I feel it is more likely to be due to smoking related damage to lungs without any super-added infection. Still, I feel you should not neglect this as weakened lungs are more prone to infection. Please see your doctor and get a chest X-ray done. Please also consider quitting smoking or at least cut down as much as possible. Best wishes.