I had alot of mouth sores when I was a kid, but once the asacol kicked in and the effects of the disease were drastically reduced, they all went away. I never once took a vitamin supplement.
I don't know how well you're feeling overall, but I encourage you to see these mouth sores as an annoying problem stemming from your poor health. If you receive a stronger treatment for your Crohn's, I believe the mouth sores will go away.
Until then, I recommend eating alot of ice, arroz caldo (chicken & rice soup), and fruits found in baby food jars.
Diagnosed with typical Crohn's at 16.
Got lucky with Asacol for a year, then even luckier with ten years of relative remission.
Now abscesses and fistulas are having an "atypical" Crohn's party around my junk.
The surgeon said it is inoperable and so I start Remicade on May 7th.