Re: Horrible stain on my tongue, please help!
What made that "stain" appear, do you relate it to something or did you just notice it one day? Does it change in colour or is it mostly yellow with a green-ish tint sometimes? Does not tongue cleaning help even a tiny bit? If it does, then you could try drinking your tea/coffee etc. with a straw. Whereabouts is that "stain", you could maybe take a picture of it. Does it change in brightness (being paler in the morning for example)? Is it more at the back of your tongue? When you scrape it off, does your tongue cleaner get yellow and would you really say it's always mucous-thick or is it more watery?
Oral hygiene has to be made into a solid every day habit, and your techniques of cleaning are of vital importance. I assume it's germ build-up, producing a lot of sulphur, making your tongue yellow-ish, which in turn is definitely acid-related. Use alkaline products daily to wash your mouth with - baking soda is good and cheap enough - especially just after you've eaten.
You could go to dental specialists just for another opinion or advice, but i'm not sure they would be able to help any more than this, if it's germ-related.