Oral sex exposes you to gonorrhea, syphilis and herpes, but obviously risk is lower than with penetrative sex. But in your case, your oral encounter was covered, which reduces the risk to practically zero.
If you still concern, you can test as follows:
-3 weeks after the encounter, for gonorrhea.
-6 weeks after the encounter, for syphilis.
-3 months after the encounter, for herpes.
If your syphilis test is negative, it would be interesting to repeat it 3 months after the exposure, as there are people that take longer to show a positive result.
All the best.