Well, you have done the right thing and got medical advice. While it is unwise to be complacent, STIs are not that easily caught, even in the very unlikely chance that an escort was infected.
Psychosomatic illnesses are quite common I think.
If you are worried or stressed it suppresses your immune system and makes it more likely that you get some sort of everyday virus. If I get stressed at work I tend to find I can get sore throats and other ailments.
Also, could just be a coincidence.
In any case, after so many tests and medical advice I would have thought it was time to stop worrying. If there was a problem I would have thought the doctor would be at least suspicious of something.