Hello, this looks like an ulcer. You can apply gel that may soothen the pain.
The missing teeth should also be addressed as the sharp edge of adjacent tooth might be the cause of chronic ulcer.
However, as this is a long standing ulcer since 6 months,I would recommend you get a consult for it so that it can be treated in a right and timely way.
Next Steps
Consultation followed by replacement of missing tooth
Health Tips
Try avoiding hot and spicy food to decrease the discomfort it might be causing.