Re: Yellow coating on tounge and enlarged taste buds.
if the coating appeared rather suddenly, it is probably the culmination of a dietary allergy -- the enlarged tastebuds you describe are part of the same phenomenon. sometimes, you can have a food allergy (and it is common to crave that food, but that is another topic) without knowing it. The body can keep inflammation in check to a point, but then if you suddenly increase your intake of that food, this is the response. the tongue is reacting to some topical insult by producing excess keratin.
If the coating is a general white coating (like you describe) often a sensitivity to yeast or mold is the root. (so large intake of coffee, tea for example can set it off -- from the spores that collect on tea leaves and coffee beans in long storage and transport to final consumption.) Relatedly, (and this is the most likely scenario) it can be a yest infection that has reached a tipping point where the body is just a little overwhelmed. This is very common, as the western diet is heavily sugar and carbo-laden. In this case, the oral symptoms appear when the entire GI tract is overloaded with yeast.
I am surprised neither md or dds suggested an rx for nystatin for you. you can control it in the natural way (by eliminating sugars, yeast, and reducing tea/coffee intake) but it takes a while - like weeks or months --and persistence! Yogurt is generally helpful in alleviating symptoms and reducing the swollen tastebud irritation. (plain, w/ acidophilus) In the extreme cases, the tongue can have a burning sensation, and yogurt give topical relief as well as helps rebalance the GI flora. the only other thing i'd suggest is ask for a sugar-free suspension if you do take nystatin -- the most commonly written rx is in a heavy sugar syrup suspension, which defeats the whole purpose!!
good luck and i hope this helps!