For itchy blisters near the vagina, the first and foremost possibility to be ruled out is of herpes blisters or sores. Most individuals have no or only minimal signs or symptoms from HSV-1 or HSV-2 infection. When signs do occur, they typically appear as one or more blisters on or around the genitals or rectum. The blisters break, leaving tender ulcers (sores) that may take two to four weeks to heal the first time they occur.
The only way of ruling it out is by getting yourself tested for genital herpes. Laboratory tests include: culture of the virus, direct fluorescent antibody (DFA) studies to detect virus, skin biopsy, and polymerase chain reaction (PCR) to test for presence of viral DNA. I sincerely advise you to consult a dermatologist and get it ruled out.
I hope it helps. Take care and regards.