Suggest Treatment For Canker Sores In Throat And Mouth

I am a 27 year old female. I suffer from large canker sores in my throat and mouth. I will get 5 or more at once. I become fatigued and it is difficult to eat or speak. This has been reacurring now for the past 6 years or so. I tested for mono the 2nd time this occured and tested negative. Round 2-3 years later the symptoms returned only much worse and this time I was diagnosed with mono. It has been nearly 2 years since having been daignosed with mono, and I still get these sores in my mouth and throat. I currenlty have 3 large ones and am having much difficulty eating, and speaking. I have seen numerous doctors had many blood tests... I don't know what else to do. Can you point me in any direction?