Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain it seems that
post nasal drip and bad breath can be very much due to
sinus infection however tonsil stones are also a common cause for bad breath..
Yellow discolouration of mouth seems to be most probably due to poor maintenance of oral hygiene leading to accumulation of debris over tongue and also can be due to infection in mouth and post nasal drip..
I would suggest you to 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..
Avoid spicy and chilled foods..
Do warm compresses around nostrils..
For tonsil stones gargle with 1:1 solution of
hydrogen peroxide and water and avoid excess intake of dairy..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora.