Suggest Remedy For Persistent Ulcers In Mouth And Tongue

hi Female 23 years old now. suffering for the past 7 years since 2009 from ulcers in the mouth area, gum, throat, and tongue area. cannot eat food and drinks liquid also. And also small painful bump show up in the fingers, hand and leg area. i visited all specialist. all the diagnostic tests performed with blood test and biopsy tests have been negative, herpes, crohns, Lupus, celiac etc.I tried immune suppress drugs also, nothing is working. Only treatment that can cure and manage symptoms has been by using prescription medication prednisone (steroid) tablets for 2 weeks dosage. The cure lasts for 3 weeks and the ulcers do come back. I got Acupuncture treatment also. Now, Dermatologist , diagnosed, it is ERYTHEMA MULTIFORM autoimmune. how long can take steroid medicine?