Hello ma am and welcome. A blister in/around the genetalia is usually first suspected to be due to herpes infection, but there are a few other causes for such a presentation as well, although less common than herpes. You have failed to mention your sexual history and also information about your partner. This information will certainly help in sucpecting herpes, or other conditions. As you have only one blister it is difficult to comment on the possible cause without a physical and laboratory examination of the same ma am. Unfortunately, you will have to wait for the reports. Wishing you nothing but good luck. Best wishes.