I have poison sumac on my private parts?

See your doctor: Because the area is so sensitive, you should start taking some benadryl (diphenhydramine) or Zyrtec. But unless it's very mild, see your doctor and ask about getting some prednisone. Prednisone is an antiinflammatory steroid that will help shorten the course of your illness. Topical steroid creams might be irritating on the area where you have the rash.