I'm going to give you the risks of giving unprotected oral sex to a penis, but please keep in mind that you really aren't at any kind of risk if it was for only 5 seconds. I wouldn't worry at all if I were you.
Giving oral sex to someone with a penis puts you at risk for oral gonorrhea and syphilis. Syphilis isn't that common, and your partner would have had to have a sore that your mouth came into contact with to transmit it. You would get a sore in your mouth anywhere from 10-90 days, with 21 days being the average. You can test for this at 6 weeks.
Oral gonorrhea doesn't usually have symptoms, but if you got them, it would be a sore, red throat, maybe a fever, maybe swollen glands. If you get symptoms, they usually appear within 7-21 days. You can get a throat swab for this at about 5 days.
There is a risk here, but oral sex is lower risk than intercourse. Given that you only performed oral for about 5 seconds, I wouldn't worry at all.