How to identify that a genital rash is herpes or not?

Painful Blisters: Herpes is a rash of painful small blister usually in clusters. It is often recurrent. Have you had blisters in the area previously? You should see a doctor ASAP for diagnosis because they are treatable but need to start treatment early in course. The diagnosis is paramount for future treatment and to prevent spread to partner and especially regarding implications of herpes and future pregnancy.