I have noticed over the last 4 or more days that I have a bitter taste in my mouth - similar to the one you get after drinking coffee or soda.  I thought maybe I wasnt drinking enough water.  I havent looked at my tongue at all, until today.  The first inch or so from the tip is the normal pink color.  After that it turns a dark yellow color.  I am thinking that has to be related to the taste in my mouth.  What can it be?  Should I be worried or go see a doctor?
Hi. Thanks for the query. Dark yellow appearance of tongue can be due to improper oral hygiene leading to deposit of debris over tongue. There seems to be overgrowth of bacteria and fungus leading to thick layer over tongue. Bad taste is also due to it. I would suggest you to start using a tongue scraper to clean your tongue. You should also gargle with a solution of HY Chat Doctor. . Use a soft toothbrush and dip it in HY