Is it possibble to have yeast on very back of tongue for a year. my doctor prescribed lozenges doesn't seem to help?

It's possible: It depends on the symptoms you are trying to treat. You could have a chronic lingual tonsillitis. Treatments for oral thrush generally need to be taken for two weeks, so don't give up early. Significant thrush would likely have been bothering such that it was treated early. If you are diabetic or use steroid inhalers or antibiotics you are at increase risk for yeast.

Yeast on the tongue: It is possible to have yeast on your tongue. Many times this is the cause of bad breath. I would suggest the you purchase and tongue scraper to help clean your tongue and also see you dentist for a medication or mouth wash that can help clean up that yeast. Many times you can clean up the yeast for awhile but it can return. If you did not take all your medication you may not have gotten all of it.