Hi thanks for your question
Ulcer(sore) in mouth are usually ophthous ulcer, caused by
stress ,spicy food and many more things and are usually self remitting, hardly need any treatment except local
analgesic and antiseptic.
Since your ulcer is nine week old it needs investigation,
Get it biopsied by some ENT surgeon to know what exactly it is
so that it can be treated accordingly .
Hope i answered your question