My dentist always knows when I have exams 'cos I get ulcers like everywhere! So yep, they are due to stress!
Remedies:
Salt water rinsing.
Bonjella
Hope you get rid of 'em soon, I know how annoying they are! I've got my brain convinced that I'm not stressed about my A2 exams even though I'm bricking it! - It's working though! No ulcers as of yet!