Welcome to the Forum and thanks for your question.  I'll be glad to comment.

Before I address your specific questions, let me make some more general comments.  The encounter you describe was relatively low risk.  As we have pointed out here on multiple occasions, most commercial sex workers do not have STIs and many CSWs do a better job or STI prevention and are less likely to be infected than casual, non CSW partners one might meet in a bar.  In addition, I was interested to hear that your partner used mouthwash following performing oral sex.  This measure has been suggested (not proven) to reduce risk for STIs during oral sex and is currently being actively studied.  If anything, that practice would reduce the risk that she was infected to even less than average. 

As for your symptoms, the are not suggestive of STI. When STIs cause symptoms they typically persist and do not go away when one is distracted.  When persons develop epididymitis, they typically have noticeable symptoms and lower abdominal pain is not part of typical epididymitis.  Your symptoms could be mechanical (i.e. muscle strain) in nature or reflect another process such as a kidney stone or even bowel problems.  While I cannot assure you that this is not an STI without testing, I find it quite unlikely and believe there are other possibilities which are more likely.  My advice is to seek the advice of your own physician who can examine you and order appropriate tests..

In answer to your specific questions:

1.  Your risk for infection is low but not zero.  When you see evaluation, I would suggest testing your urine for gonorrhea and chlamydia, as well as performing a urinalysis (which may be helpful for diagnosing things like kidney stones).

2.  If your symptoms persist or worsen, I would seek medical evaluation as a general recommendation.  I am not so worried about STI.

3.  Your symptoms are not particularly suggestive of epididymitis. 

I hope these comments are helpful.  EWH

Thanks for the additional information and your patience in waiting to see if your symptoms would change.  The more information you provide, the more confident I am that the discomfort(s) that you are experiencing are not due to STI.  I would not worry.  In answer to your specific questions:

1.  Yes, the lack of progression (as well as the nature of the pain you describe) it inconsistent with an STI.

2.  The mechanisms by which gonorrhea leads to arthritis and to epididymitis are different.  If you had epididymitis your discomfort would be progressive and you would almost certainly have discomfort on urination or a penile discharge.

3.  Yes, my advice would be to relax and move forward without concern.

4.  If this was epididymitis, it would have progressed and would not have been intermittent.  What you describe really does not sound at all like epididymitis.

Hope this helps.  EWH

Thanks again for the update.  That your symptoms have persisted suggest that you would benefit from evaluation.  In my opinion however, evaluation for STI is not needed for all of the reasons noted above which I will not repeat.  In answer to your final questions (as per Forum guidelines, this thread will be closed after this response and without further replies).

1.  Yes, I would discard the possibility that these symptoms are due to an STI.

2.  Correct.  I see no reason to abstain from unprotected sex with your regular partner.

3.  Yes, it is fair to mention this to your doctor, after all the possibility is prominently on your mind.  I would urge you however not to accept treatment unless your doctor also chooses to test. 

Thanks for your thanks.  I hope this problem resolves quickly for you.  Take care.  EWH