The blisters can be caused by the vibrator if you're not using enough lube. It can also be contact dermatitis, the skin can blister by coming into contact with cosmetic, detergent, solvent or other chemicals. Dermatitis herpetiformis, can also be possible, though its rare, and I've never heard of it happening vaginally. DH is a skin disorder thats associated with celiac disease, in where blisters occur on both sides of the body. Chronic bullous dermatosis, does occur on the genitals, but its a childhood disease.

Avoid taking baths, using a vibrator, and try to let them heal. If they continue to be there, after several months, go back to your doctor and see if its something you should be worried about. But if your doctor says not to worry, don't worry. If you're really concerned get a second opinion before getting paranoid its something else.