Hi Ashley,
In my opinion, it's a sign not so much that a flare is starting, but that you're in a flare. I feel that the vast majority of the time, these ulcers are due to vitamin deficiency which is due to malabsorption which is due to inflammation in your intestines.
You'll see some people report that the ulcers go away with treatments such as entocort. My guess is because that takes away the inflammation which, as long as there is proper diet thereafter, allows uptake of nutrients again.
I'd suggest a high quality B Complex vitamin like Dexky above put forth. If it was me, I'd also be supplementing additional B12 as well.
Good luck!