Thanks for your question. There are a few different things that this could be, and your doctor
will be able to help you more to get more information and some treatment. First, it is possible that this is debris and old mucosa from the top of your tongue. If this is the case, then brushing your tongue as well as your teeth twice a day is one of the best things to do to help with the coating that you are describing. If you have been doing this already and still have some symptoms, then it is possible that this could be a sign of thrush. Thrush is a fungal infection that is common in those who are immune compromised or have some other reason not to have a normal immune response in their mouths. A common reason for otherwise healthy people to have thrush is some of the steroid inhalers that are used for asthma
and other pulmonary problems. That is why your doctor will advise you to rinse your mouth after each use of such an inhaler if you have them. There are other, less common, reasons for a white coating on your tongue. Again, please speak with your doctor.