Why can't you go for a blood test? There are clinics that can test you anonymously. I doubt you contracted anything if it was protected sex (unless you kissed and you both had open mouth sores or cuts).

Just get tested for your own peace of mind. You'll never get it out of your head if you don't. Talk to the clinic doctor and follow their recommendations on how many tests to take and how far apart.

Also, I would avoid prostitutes, if I were you. This doesn't seem to be a good experience for you.

The illness could have been something you ate or even a stomach virus.