Tongue & Mouth soreness. A remedy.

I have been facing tongue soreness for 7 months. I got mouth ulcers & tongue soreness 8 months ago. So I used candid mouth paint oral thrush and soreness got less severe. But, the problem was not resolved completely. The problem is aggravating when I eat fruits like banana and grapes. I stopped taking these fruits for more than 6 months and did not face the issues during this period.  I ate one banana last week and Cysts(ulcers) are appearing on the walls of mouth and inside lip area. I am facing burning sensation on tongue. Before facing this problem, I have used Vitamin C chewable tablets for more than 6 months because my orthopaedic doctor suggested that medicine for costo condroitis. Now, because of this soreness problem I cannot consume this medicine. My food intake has less source of vitamin B12 (I consume only eggs. No other non-veg foods). Please suggest a remedy.