What is the cause of a hurting, nasty taste, white colored tongue?

Thrush: The most common cause for what you describe is candidiasis or thrush. It is a yeast infection that can be treated quite easily. If you are a high risk lifestyle, i would also get an HIV test just to cover all my bases. Otherwise, some Nystatin should do the trick.

Brush tongue: Frequently this is caused by food and bacterial debris on your tongue and it can be removed by brushing or using a tongue scraper. If the pain persists then see tour dentist.