Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain burnt or scalding feeling of the roof of mouth and tongue after having a history of productive cough and sore throat can be due to inflammation of the mucous membrane of tongue and palate and it can be secondary to allergic reaction of medicines or due to dry mouth caused by mouth breathing or dehydration which is common in sinus congestion as breathing through nose becomes difficult due to congestion.. Nothing to worry, consult an Oral Physician and get evaluated and in case if it is due to allergic reaction to any medicine change of medication will help.. In case of dry mouth chewing sugar free chewing gums, drinking plenty of water, taking salivary substitutes known as Artificial saliva agents can help.. Consult an Otolaryngologist and get evaluated for productive cough and sore throat as cough and phlegm continuing for 3 and hald weeks is not normal and can be a sign of lower respiratory tract infection which should be taken care of.. As of now you can chew sugarfree chewing gum and gargle with a numbing mouthwash containing Lignocaine for relief from burning especially during meals. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.