It is possible to get small ulcers or blisters as a dermitological response to some foods and acids. This is a pseudo food allergy response. I do not know if this is what you have, but if the only variable different is the Big Red gum... stop chewing it. It can take a few days for the blisters to subside after they have been formed. So relax, and see what happens. If it starts to get worse go to the doctor.