I have been getting small fluid filled vesicle-like blisters in my mouth beyond my wisdom teeth. They are easy to burst but they keep returning. I am 51 years old. I do not take any prescription medication or OTC meds on regular basis. I have never smoked.
You are having pus in those blisters. Probably arising in relation to a decayed tooth. Go to a dentist, get a X-ray done and plan accordingly after finding out the affected tooth.