Sin in that area is really sensitive, and the own physical action of performing oral sex and licking could be the response. Definitely is not an STD. But you were exposed to gonorrhea, syphilis and herpes through the oral sex, so it would be interesting to test as follows:
-3 weeks after the exposure, for gonorrhea.
-6 weeks after the exposure, for syphilis, and if you get it negative, repeat it 3 months after the encounter, as there are people that take longer to show a positive result.
-3 months after the encounter, for herpes.
Anilingus can expose you to these ones as well, but it's also a source of other infections like E.coli and Giardia.
All the best.