I'm coming into this a bit late, but someone might find the following helpful:
I have a condition call Oral Lichen Planus, which involves frequent small sore blisters (not really ulcers) on the mucus membranes of the mouth, accompanied by very tiny, quite long random ridges across the inside of the cheeks.
There is no known cause for this, but it is thought to be stress-related. I developed it about 13 months ago, during the most stressful house move I have ever done. I was also diagnosed Type II just after this started, with fasting blood glucose at 9. I haven't asked whether it might be related to the diabetes.
There is no cure; apparently it can (and should) just go away of its own accord. It can be aggravated by eating smoked foods, cheese and almonds, also very spicy foods.
Mine does seem to be getting better now that I am much less stressed, but (eg) smoked mackerel will make it flare up again.
This is the mouth version of a condition called Lichen Planus, which can occur elsewhere on the body as small subcutaneous lumps. I don't know much about this (haven't got it!) but there's plenty of info if you Google.
Viv 8)