I noticed a few weeks ago, a dark coating towards the back of my tongue, I went to my doctor and she said to gargle with water, proxide and brush, I brush all the time. and I have been do what she told me to do, but it isn t going away, I am always coughing and gagging because of it. She said I don t have thrush and it should clear up. I was taking a med. called Bentyle that made my mouth real dry, so I stopped taking that, im drinking tons of water, Please help