Parents of a 6-year-old child are concerned about their child refusing to eat and having grey-and-yellow coating in the oral cavity. The symptoms are observed over a period of one year. The child complains of sharp dryness and burning pain in the mouth. The anamnesis states chronic bronchitis and systematic treatment using anitibiotics. Objectively: swollen and hyperemic mucous membranes of lips and cheeks are covered in yellow and pale-grey coating. There is coating on the tongue, which is connected with the tissue, cannot be removed and has infiltration basis. What is the most probable diagnosis?