Hello sir,       Hope you are doing good. It may be due to dirt (plaque) in the mouth which may cause bad breath. It cannot be removed by brushing.please visit us to get it cleaned by scaling (professional scaling). And please do get checked by general physician also whether you have any gastric problem which would also cause bad breath.

Bad breath or halitosis could be of other reason than the teeth. Mostly GI disturbance, sore throat, tonsillitis , xerostomia, etc. Sometimes the tongue traps food and bacteria. Try to get it checked and clean the tongue with a seperate  brush after you finish tooth brushing.