Get a professional cleaning done to remove any deposits that might be causing bad breath. Brush twice a day , clean your tongue every night and use mouthwash post brushing at night. Avoid 1)food with too much sugar 2) smoking 3) alcohol 4) onion or garlic that can lead to bad breath. Rinse thoroughly after every snack/meal.

The phenomenon of olfactory adaptation is the one responsible for diminished sense of the same smell when exposed for a long time. This is meant to relieve the burden from the brain, and to give a practical example, if you apply perfume on your body you will feel it for some time but after that you don't feel it directly but others can always make out. So please don't ignore the problem of bad odour from the mouth only because you can't feel it. You will require professional cleaning by a procedure called as ultrasonic scaling followed by guidance about proper brushing technique to improve your oral health. Regards