You don't say, but I presume you're male. (I suspect few ladies would compare their pain to blue balls.)
Gay men are at risk for any number of enteric infections, i.e. those transmitted by exposure to feces, and you probably could have acquired such an infection from that exposure, such as
campylobacterCampylobacter enteritis,
salmonellaSalmonella enterocolitis, or shigella. Or an enteric virus. On the other hand, there is no particular reason to assume your symptoms were acquired at that time, and your symptoms may not be an infection at all. Appendicitis always is a possibility for unexplained low abdominal pain, for example.
So keep your appointment (or even move it up, if your pain becomes especially severe or if you develop a fever). In the meantime, this doesn't sound especially worrisome.
Good luck-- HHH, MD