Based on your description, you could be experiencing an STD, there are four possibilities according to the WebMD website.
The conditions associated with your symptoms are:
Gonorrhea, Chlamydia, Lice or Crabs.
Here is the website if you want to check it out yourself (I would definitely see a doctor right away):
See a doctor. That is your best option. You could have a STD. It is hard to say without getting a sexual history and seeing the rash.