Receiving oral sex puts you at risk for gonorrhea, chlamydia, NGU, syphilis and genital herpes type 1 (if you don't already have oral herpes type 1).
Oral sex is lower risk than vaginal or anal sex.
You can test for gonorrhea, chlamydia and NGU at a week. You can test for syphilis at 6 weeks.
If you don't get any symptoms, I wouldn't bother testing for hsv1. You might already have it orally - 67% of the global population under 50 has it, and the test misses a full 30% of infections, so it's not all that reliable. If you get any sores or blisters, get in to a doctor within 48 hrs and get that cultured. Don't do anything to it - don't put any meds or creams on it, don't try to pop it, just go see a doctor.
Remember that your risks are pretty low. Most doctors don't think that one act of oral sex warrants testing, but if you have a regular partner or you're anxious, you can test for peace of mind.