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.
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):
http://symptoms.webmd.com/symptomchecker
Good luck