Talk to Gastroenterologist on Reoccurring Mouth Ulcers

I have been facing this problem for the last 8-9 years as long as I remember. I get multiple mouth ulcers, usually 7-8 (at worse even 15+) altogether and they make my life hell for 7-8 days and then they heal. after four to five days, new set of ulcers at various spots start appearing and the cycle continues. In short, i have multiple mouth uclers for around 3 weeks in a month. I have been to multiple doctors, dentists, homeopathic, herbal. but all in vain. Can anyone suggest from their experience or any doctor who thinks he/she can treat? I have tried almost all oral gels and mouthwashes. my issue is WHY DO THESE ULCERS KEEP ON COMING. I am in serious pain and trouble, pls help