So to clarify - you think she she got vaginal secretions on her hand and that's how they got on your penis? Or did they somehow get on your penis in another way?
If it was a handjob, there's no risk here for an STI. Touching herself than touching you is not a way infections are transmitted. Also, given that you only seem to notice symptoms when you think about the encounter suggests that it's anxiety, and not an actual infection.
However, you can get an infection in your prostate without having any kind of exposure, so definitely get checked out if you are having pain and urinary frequency. Perhaps you have a UTI or a prostate infection. It might be something as simple as dehydration or irritation from too much alcohol or caffeine and not enough water, too.