I Have Recurrent Mouth Ulcers For About A Year... On

I have recurrent mouth ulcers for about a year... on a week or so and then off . They are so painful that I have been unable to sleep at times or eat and have lost 20+ lbs. I have used a special mouthwash and Lidocaine and a trimenacone (?) dental paste.. also several times prednisone.
I have had extensive dental work and implants done in the past year. Everyone says "stress". I am Female 75 years old , there is not much stress in my life now, ..is it time to have tests done ? I have seen, my primary MD, 2 ENT's, an urgent care MD ( I was desperate) , dentist and my dermatologist.
Research online suggests a possible autoimmune problem. I don't have any other symptoms except the apthious (sp.) ulcers.
Thank you,
Leah Kinnear
Any suggestions?