Dear Welcome to HCM We understand your concerns I went through your description. As you had checked for the presence ofany STD and the result was negative, then we can rule out STD. Then the small red pustules should be real pustules which normally appears on sensitive skin during winter season. Just watch out whether it spreads into other parts. If it does, you should consult a dermatologist for expert advice. For the time being, you can wash your private area with mild soap and apply some skin nourisher creams and keep the area airy for some time. Can also use lacto calamine lotion. Wait for two three days and the blisters should subside. I hope I am able to answer your question. Available for further assistance. Get well soon.