Talk to Gastroenterologist on Reoccurring Mouth Ulcers / Canker Sores

I have been having this unexplainable problem for the last 15 years. For around 3 weeks in each month, I have multiple ulcers/canker sores. They are usually 4-5, but at times go upto 10+ at the same time. once they all get cured in around 2 weeks, I get relief of a week or two MAXIMUM and new ulcers start coming out. The ulcers are painful and burning, makes my life hell as I cant eat, talk and even sleep properly. I have been to multiple dentists, GPs, internal medicine specilaists, endocrinologists, homeo, herbal and Gastroenterologists (Dr Sajid Nisar also couldn't understand and said he had no clue).

is there any doctor who had any experience of successfully treating such case or thinks he can diagnose and provide solution, PLEASE help