Irritation and sometimes a blister or rash in vaginal area during menstrual cycle. has been tested to chlamydia and was negative. ?

Herpes is possible: If you are having blisters, the first thing to consider is herpes. You can have the blood antibodies checked any time or get a culture of the area when you have the symptoms.

Need more testing: If this is a recurrent problem, you should be tested for herpes. See your gyn if another episode occurs and specifically ask about herpes testing.