Hi. Ammonia like smell through nose that others cannot experience and no history of bad breath seems consistent with a condition known as Phantosmia.. It can occur due to a number of conditions like nasal infection and polyps, migranes, Oral and dental infection, smoking habit, condition related to Nervous System etc.. I will suggest you to consult a Medicine Specialist or a Neurologist and get evaluated and along with clinical evaluation investigations like Nasal endoscopy, MRI, CT Scan etc can help in diagnosis and treatment can be planned accordingly.. As of now you can do saline nasal irrigation, steam inhalation with few drops of Eucalyptus oil in water,chew flavored sugar free chewing gum and limit intake of high aroma foods like onion and garlic.. Hope I have answered your query. Let me know if I can assist you further. Regards, Dr. Honey Arora, Dentist