Hi.. Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns.. As per your complain it seems that the white patch that you have developed under your tongue is either a large traumatic ulcer or can be a Major Apthous Ulcer.. As it is just one week you need not to worry as it does not seems to be anything serious.. I would suggest you to start apply a numbing gel containing Lignocaine or Analgesic gel containing Choline Salicylate over it.. You should also apply a steroid ointment like Triamcenolone Acetonide.. Take a multivitamin tablet daily.. Take anti-inflammatory painkiller like Ibuprofen.. Avoid spicy and hard foods and take a soft diet to avoid trauma or irritation to the area.. You should also do cool water rinses to reduce inflammation.. You can also do alcohol free antiseptic mouthwash to avoid infection.. In case of no resolution in a week consult an Oral Physician and get evaluated.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.