Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain the dark coating of tongue seems to be due to Black Hairy tongue that is a harmless condition and can occur due to trapped debris over the tongue papillae as well as overgrowth of bacteria and fungus.. There can also be due to overgrowth of papillae due to non-shedding of the papillae.. Excessive intake of tea and coffee, tobacco and medicines like Pepto-Bismol can also be a cause.. Proper Maintenance of oral hygiene and regular cleaning of tongue using a tongue scraper and gargle with 1:1 solution of hydrogen peroxide and water can help.. You should limit taking tea, coffee, tobacco intake should be stopped.. You can also clean your tongue using a soft toothbrush dipped in solution of hydrogen peroxide and water and gently brushing the tongue.. Eat more of hard foods.. You should also consult an Oral Physician and in case if there is overgrowth of bacteria or fungus medications like antibiotics or antifungals can help.. The burning sensation of tongue can be due to Apthous stomatitis and can be due to deficiency of iron and vitamin B12, oral infections etc.. You can gargle with numbing mouthwash, take multivitamin supplements, take Ibuprofen for pain relief, suck ice and gargle with cold water.. Avoid spicy food.. Hope this information helps.. Thanks and regards. Dr. Honey Nandwani Arora.