Hi.. Thanks for the query.. As per your complain Sinus Infection or Sinusitis is one of the most common cause for post nasal drip and bad breath.. So you need to first of all get a proper treatment of Sinusitis done.. For this you should consult an Otolaryngologist and get evaluated and a thorough clinical evaluation and investigations like PNS view x ray or MRI scan can help in diagnosis and treatment can be done accordingly. You can be advised a course of antibiotics, anti-inflammatory painkiller like Ibuprofen, decongestants like Pseudoephadrine, do saline nasal irrigation, steam inhalation and use a humidifier in your room.. You can also be advised decongestant nasal sprays containing Xylometazoline or Oxymetazoline.. Taking steam inhalation with a few drops of Eucalyptus oil in boiling water can refresh your breath.. For masking bad breath you can chew flavoured sugar free chewing gum.. Gargle with flavoured antiseptic mouthwash.. Refreshing mouth sprays can also be used.. Chewing Cardamom is also helpful.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.