In any case, given the sexual exposure with a partner of uncertain STD
status, and absence of the usual explanation for
such symptoms (i.e. no UTI), you are right to be concerned about the possibility of an STD, such as gonorrhea, chlamydia, or herpes. That said, yeast infections commonly cause such symptoms. Perhaps most reassuringly, most such symptoms end up with no obvious cause -- perhaps minor physical irritation from sex, for example.