Oral sex exposes you to gonorrhea, syphilis and herpes, but the risk is very low. You should test as follows:
-Gonorrhea, 3 weeks after the exposure.
-Herpes, 3 months after the exposure.
-Syphilis, 6 weeks after the exposure, and repeat the test 3 months after the exposure if in your first one you get a negative result.
All the best.