Any sore in the mouth for more than 2 or 3 weeks which does not heal on its own needs to be evaluated by a professional. Here in the US, an ENT who specializes in treating oral cancer patients is usually the best option. Only thru a biopsy can it be determined for certain exactly what the sore/spot/lump is.

I highly recommend seeking out an experienced ENT to get to the bottom of whats going on in your mouth! It could be nothing serious, there are many things besides cancer mouth sores can be. But, if your sore does turn out to be cancer you will want to get it diagnosed and get treated before it progresses. I cant stress enough how important it is to get this figured out ASAP. Dont waste your time with the wrong kind of doctor. Here in the US, orthodontists do kids braces, most would have no clue how oral cancer tumors present themselves or its symptoms. Im sure this is the same everywhere, not all doctors or dentists know enough about oral cancer to effectively help someone who possibly has it. Its very rare for them to see it so they arent able to recognize what needs further evaluating and what doesnt. With that in mind, if you are being evaluated by someone who is not familiar with oral cancer or unusual mouth tissue issues then its a waste of time which could be a major mistake if whats going on is anything serious.

Hopefully what you have is not anything serious. Please dont play around, get examined by the correct doctor. Best wishes!