All STD transmission is rare with cunnilingus (oral contact with female genitals). Even with prolonged exposure, e.g. to orgasm, it rarely happens. Probably some cases of herpes and gonorrhea occassionally are transmitted, but very rarely. But certainly there is no risk from the fleeting contact you describe. HIV has never been known to be transmitted by cunningus, in either direction.
Here is another thread that explains the transmission biology of STDs in more detail:
http://www.medhelp.org/posts/show/1119533
So please accept the reassurance and don't worry about this event. If and when you start having intercourse, you can begin to legitimately worry about STD risks -- and even then, you'll keep it to a minimum by using condoms consistently.