Have you been to the doctors and been diagnosed with anything like acid reflux?
Hello,
The smell is due to gases produced by the action of certain bacteria on protein and other substances. These bacteria may be present on your tongue, in your mouth, Gums , nose, tonsils, esophagus or stomach. Tonsils are lymph nodes present in the mouth which when inflamed and calcified (tonsillitis with tinsiloliths) also releases foul smell.
To confirm the diagnosis you need a detailed ENT check up and a swab culture of the nasal swabs and discharge done.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.