CPPS is a possibility (if you have not, take a look at the write-up on
Wikipedia, it is quite good) and for better or worse, CPPS is not associated with STI, does not respond to STI therapy, and is not associated with harm to sexual partners. it may linger however.
My advice is as follows- I see little potential benefit for you from further testing for STIs, or to occur with further treatment of any sort.