Hi, please relax & don't be so alarmed. It is really good that you practice safe sex
. Common causes of vaginal blisters include: friction, infected hair follicles, ingrown pubic hairs or blocked sweat glands etc. However they may be a hallmark of STDs like herpes
. Your's seems to be a simple one. If the problem persist or recurs then please consult a gynaecologist. Take care.