Please do not jump to the diagnosis of Cancer just like that because even a doctor needs a biopsy to say that for sure.
Please mention the duration since the injury occurred. Any traumatic injury in the oral cavity normally is within 7 to 10 days unless complicated by secondary factors. If there is a sharp edge on the tooth it will not let the lesion Heal because it will be a source of chronic trauma because whenever the tongue will move it will come in contact with that sharp edge. Get the tooth evaluated by the dentist and get it treated appropriately so that the sharp edge should not be a botheration.
You can continue taking multivitamins but please understand that no
vitamin has any role whatsoever in the healing of an ulcer which has already formed. Multivitamins maintain general Physical health so their use can be continued but the role of any medicine that you take has to be understood clearly.
You can apply anaesthetic ointments like dologel CT for temporary symptomatic relief.
Please post a clinical picture for a more rational opinion.
Regards