Never think about symptoms because sometimes stds don't show any of them.
Oral sex exposes you to syphilis, gonorrhea and chlamydia. It would be good to test for those ones three weeks after the exposure.
HIV risk through oral sex is negligible. For the rest of the STDs, I agree with my colleagues about herpes. You can test for syphilis, gonorrhea and chlamydia after three weeks, but if your results are negative, it would be good to test again after 3-6 months, because there are people that take longer to give a positive result.