Very sorry to hear about that . Well recurrent mouth ulcers as you would have been told by your doctor ,are caused by a lot of different causes e.g poor oral hygiene, issues with gastric reflux and waterbrash at night, vitamin / mineral deficiencies e.g zinc , B12 deficiency , certain autoimmune conditions like SLE, Crohn's disease, Behcet's disease, celiac disease etc.
So it needs extensive work-up which obviously is time taking and frustrating too.
I would advise you following measures for your problem , it should help you with this ;
Meticulous oral hygiene - tooth brush twice a day esp before you sleep, cleaning your tongue too, using dental floss and mouth wash to reach every corner of your mouth.
Antacids like omeprazole if you have reflux issues
Taking probiotics can be helpful.
Vitamin B12 and mineral supplements
Triamcinolone acetate topical application to the ulcers really helps heal them quickly.
You may also use nilstat oral swish & swallow solution for these.
Avoid any drug / food that apparently seems to be a trigger.
I hope you find these tips useful.
Wish you all the best.
Let me know if you have any more queries.