Welcome to our Forum.  This is a challenging problem and one that we see from time to time.  I will try to help.  You have proven that you do not have a recognized STI as a result of the encounter that you describe and thus I can say with confidence both that you do not have an STI that needs treatment (you do not say if you have tried antibiotics or not but I suspect you have) and, equally important, you are not at risk to future sexual partners.  This is not meant to discount your symptoms but rather to assure you that they are not an STI or a risk to partners.

As far as what is going on, you may have CPPS (Chronic Pelvic Pain Syndrome - it is well described in Wikipedia) or some other process but what you do not have is an STI.  Occasionally specialist such as us do see patients who have chronic non-infectious urethral discharge.  Unlike you, most such patients do have signs of chronic inflammation as well as recurrent or chronic urethral discharge.  What we can say with confidence is that such patients, following extensive work-up of the sort you describe, do not go on to develop STI complications, nor are their sexual partners at risk. 

My advice to you in this difficult and challenging situation is to find a health care provider who you feel comfortable with and are able to communicate with and to commit to observing this process over time, without further diagnostic tests or treatment unless something changes.  In many persons in similar situations the symptoms resolve on there own while in others, over time, clues develop which lead to an accurate (non-STI) diagnosis.

I hope this perspective and suggestion is helpful to you.  EWH

I really want to think it's nothing to worry about, but it seemed too much of a coincidence that it started not long after the encounter and these stomach issues that have now started in both my current partner and myself are worrying (along with the pain in my toes)!