Thanks for your query.
The aphthous ulcers
can be caused by physical trauma, stress, lack of sleep, sudden weight loss
, food allergiesdue to decreased immunity,and deficiencies in vitamin B12
, iron, and folic acid
and even fungal due to candid infections.
Since you have taken B-complex if the ulcers are due to the deficiency they should improve.
I would suggest you to continue B-complex with folic acid and locally apply Stomela gel or Orasep -OS locally to the ulcersin the mouth.
If it does not improve in 2-3 days please consult your physician and get treated.