Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain it seems that the symptoms of moyth ulcers with severe pain and sensitive gums can be due to causes like aggressive form of Apthous Stomatitis leading to Apthous Ulcers and as you are three weeks post tonsillectomy they can be due to allergic reaction to medication given to you post surgery.. Other causes of Apthous ulcers can be of iron and vitamin B12, stress, physical trauma to the tongue, allergies, acid reflux etc.. It can also be due to Herpes virus infection or Bullous Pemphegoid.. You should consult an Oral Physician and get evaluated and a thorough clinical examination and investigations like Blood tests, oral swab culture, microscopic examination of scrapings from the lesions and even biopsy can be advised for confirmation of the cause and treatment will be done accordingly.. As of now start gargling with numbing mouthwash containing Lignocaine to relieve pain especially before meals.. You can also take Ibuprofen to relieve inflammation and pain.. You should avid hot and spicy food.. Suck ice and do cool water rinses.. Drink plenty of water. Take Vitamin B complex supplements.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.