Hello, I Have Been Having A Bad Taste In My

Hello, I have been having a bad taste in my mouth since September 2015 which started following the removal of a wisdom and back lower tooth. I have had lots of dire rent medication from doctors that has not helped. Yesterday I noticed a white spot near to the back of my mouth on the same side I had the extraction when I touched it the head was soft and yellow grunge came out. I still have the bad taste. What is this?