What's the difference to a pimple and herpes on your genitals? I have a whitehead down there but I also have a cold sore, do I have genital herpes?

Could be either. Genital herpes typically consists of one or more painful group(s) of blisters on a red base. Sometimes the blisters look like "whiteheads". The only way to know for sure is to have a culture done by your doctor or a dermatologist.