Oral sex exposes you to syphilis, gonorrhea and herpes. As you said, you didn't see any herpes signal, so I think you can forget about that one.
You can test for syphilis 6 weeks after the exposure. If you get it negative, re-test after 3 months, as there are people that take longer to show a positive result.
For gonorrhea, you have to test 3 weeks after the exposure.
But I must tell you that the risk is really low. STDs are difficult to catch, even with sexual intercourses. But sometimes, they don't show any symptom at all, even after a long time, so it's good to test after exposure with people we don't know.
If you have no symptoms, don't worry