Hi as an Oral Physician consultant oral ulcers can be symptoms to multiple underlying systemic problems.. often multivitamins are randomly prescribed without a thought and hence diagnosis is left unattended.. in your case since is more than 3 months I would recommend you why don't you visit a specialist in same field Oral medicine who would be able to evaluate your general health and co relate it with your ulcers... As for your knowledge ulcers can have multiple causes... different types of anemia, iron deficiency, zinc deficiency, vitamin B12 deficiency, constipation, adverse effects of concomitant medications, gastrointestinal disorders, parasitic infections, viral infections, food allergy, autoimmune diseases, psychosomatic disorders... and so on And let me inform you all causes are very common... unfortunately because of lack of complete knowledge only few causes are highlighted and hence patients are mostly left with chronic ulcers... In my opinion with your details I doubt it's an oral cancer but I will strongly recommend you if you can approach an oral medicine specialist for same

Hi.. mouth ulcers are common in times of stress along with faulty dietary habits such as excessive spicy and oily food lacking in nutrition.. Sleeping right, regular exercise and healthy diet can help one beat stress related effects on the body .. Cancer is generally a non healing ulcer.. etc. Do leave your fears behind and consult an oral and maxillifacial surgeon( dental specialist) for an appropriate diagnosis.