Brief Answer:
Most probably aphthous , if single- biopsy

Detailed Answer:
Hi.
Please give details::
Since how long have you got this problem?
Is it recurrent meaning coming again and again?
Do you have any [problem related to your stomach/ intestines / stool?
Are these small, less than 3 mm and painful?
Or large ?
Which place/ area of the the mouth?
What is the treatment you have taken?
Are these related to your stress?
Do you take tobacco/ cigarette or any such habits?
Are you diabetis or have any other medical problem?

If you answer these correctly and post a good quality clear photograph attached to this query, I can help you better.

These may be aphthous ulcer and the exact reason although not know the treatment is empirical but helps many , many patients.

Always take mutivitamins and probiotics.
If this is a single one , one has to get the biopsy done.

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