There are some great threads on "Vapers Mouth" do a search for this term, if you are
vaping at too low of a temp you can have incomplete combustion which leaves a film, also you should sip between vapes and use a good mouthwash with alcohol to break up the film.
This happens to all of us at first and it is depressing, but with vigorous oral care and clearing the sinuses you will be back enjoying you vape in no time!