I've been battling geographic tongue (ulcers on tongue) for years. It comes and goes. I was told that it has something to do with yeast overgrown, stress and low B12 etc. It got much better after I started eating more raw and fresh food and less processed food. Once in a while when I slipped, I'll get a small ulcer, but it'll clear up in a couple of days as soon as I stop the bad food.
Couple weeks ago, I started taking 50mg of Iron along with 120mg of Vitamin C. After 3 days, my tongue went out of control. I have stopped the Iron, and continue to take and up my Vitamin C to 1g/day. My tongue has gotten better, but not completely back to a healthy state. I wonder if it has something to do with the Vitamin C.