I am having mouth ulcers for some years now, if one gets cured another pops out in weeks or months, how can i permanently cure them?

You can read this link for more info: https://my.clevelandclinic.org/health/diseases/10945-canker-sores. I would advise a trial of Centrum Silver MVI one a day for 3 months, especially if you are quite selective with your foods. You can drop the MVI after 3 months if you do not see any effects. This is based on my personal experience.

A diet with a lot of acidic foods should be eliminated. Vitamin deficiencies if any cured, lack of sleep addressed, any bacterial or fungal infections cured. Also stress is a big factor, eliminate as much of these as possible, but no guarantee of permanent cure.