Hi.. Thanks for the query.. Bad breath also known as Halitosis can occur due to a number of causes like poor oral hygiene, oral and dental infections,post nasal drip, sinusitis, acid reflux,respiratory infections, diabetes etc.. If you brush too much and for long duration then teeth can become sensitive, so it is advisable to brush your teeth twice a day only and that too not more that 2-3 minutes.. You should consult an Oral Physician or an Otolaryngologist and get evaluated and a thorough clinical evaluation and investigations depending upon suspected cause can help in diagnosis.. Treatment of underlying cause will relieve the symptoms.. As of now you should start gargling with a flavoured mouthwash twice a day.. You should chew flavored sugarfree chewing gum.. Do warm saline gargles twice a day.. Limit the intake of high aroma foods like onion and garlic.. Drink plenty of water and maintain a good oral hygiene.. Hope this helps.. Regards.