[Tasteless]

I have been unable to taste normally for about 2 years due to an unusual sour taste. I have lost a great deal of weight because when I eat it simply doesn't taste good so I just stop eating! The doctors can find no medical reason I have this taste. We have even done the elimination process of certain medications, foods, etc. The doctors seem to be familiar with a metalic taste, but not a sour taste.
Does anyone have any thoughts, ideas, etc. as to what could be causing this? Thank you for any help.