Hi. Thanks for the query.. It looks like a traumatic ulcer that might be caused due to gum injury with Clarinet paying also.. Secondly it is also possible that you have injured your gum with toothbrush or any sharp food.. Nothing to worry, start apply Lidocaine gel over it and along with it antiseptic ointment like Chlorohexidine or Metronidazole containing ointment can be applied that are suitable for oral use. Do warm saline gargles. Avoid playing any oral instrument to avoid chances or re-injury.. Take soft non irritant meals.. If it still worsen consult an Oral Physician for an in person examination.. Hope this helps.. Regards.