Hi.. Thanks for the query.. As per your complain it seems like white bump under the tongue along with small rash like patch on the cheek seems to be due to apthous stomatitis leading to apthous ulcers or canker sores.. The symptoms that you are explaining are consistent with the same.. It can be due to allergic reaction to any food or medication while can also be due to burning with very hot foods or chemicals like concentrated solution of mouthwash.. Vitamin B 12 or Iron deficiency can also be a cause.. I would suggest you to consult an Oral Physician and get evaluated.. You can be advised analgesic gel containing Choline salicylate or Lidocaine.. Take Vitamin B complex supplements daily for atleast 15 days.. You can do warm saline gargles.. Gargle with 1:1 solution of benadryl and milk of magnesia.. You can suck ice pops and do cool water rinses.. Take soft and bland foods and avoid spicy and sharp foods... Hope this information helps.. Regards.