HI, thanks for using healthcare magic Halitosis (bad breath) is most often related to dental issues though there can also be other causes as well. If you are flossing and brushing 2 to 3 times daily along with mouth wash and the dentist has ruled out any other possible lesions in the mouth then other causes would need to be considered. Since you have a post nasal drip then this may be a cause as well and can be treated with nasal sprays along with antihistamines and decongestants. The anti histamine/decongestants would be over the counter under allergy or cough and cold meds. Topical steroid sprays such as nasocort, nasonex, flonase or rhinocort can be used to help decrease the mucus as well. These may require a prescription from your doctor. I hope this helps