The only thing I can think of is syphilis, or a fungal infection. A doc can test you for syphilis, and should be able to tell if its a fungal infection.
A syphilis sore can linger for up to about 4 weeks.
You really do want to get this tested, ok?
AJ
It could just be a rash. Don't mess with it. Go see a dermotologist. If its been there for two weeks, its likely to be nothing.