Considering the details provided I would like you to keep a watch on symptoms like fever on and off, weight loss and blood in sputum. If not, then its not much to worry about. Pollution, work place exertion, domestic pollution are important factors causing this. Drink warm water regularly, avoid oily deep fried food and practice meditation and pranayam daily. Take care!

Get your sputum examination done by nearest lab. It could be any bacterial infection. Are you suffering from recurrent cold and cough? Are you living in an area with too much of pollution? Are you working at some place that have minute particles? Answer me these along with your sputum report to guide you properly.