Welcome to our Forum and thanks for a question.  As you point out, this is a frequent concern.  I hope that the comments that I make will reassure and help you.  The exposures that you describe were virtually no risk for HIV and very, very low risk for syphilis.  If I were you I would not be worried at all.

First condoms.  Studies of condoms for HIV prevent show that as long as condoms are used throughout sex and do not break (condoms do break, about 1% of the time) they provide close to complete protection.  In large studies there are sometimes infections which occur but the same studies also show that study participants, who can only be followed based on their own reports of whether or not they used them, sometime do not report their failure to use condoms correctly (perhaps they are embarrassed that they did not use a condom) and there is no way to prove that they did or did not.  Since most people (even CSWs) do not have HIV, since most exposures to infected partners do not lead to infection, and since condoms work well, I would urge you not to worry about the possibility that a condom did not protect you if used throughout sex.  They remain the single best way to prevent acquisition of STIs.

Secondly, oral sex is very, very low risk.  Although there are a very, very small number of instances in which HIV appears to have been acquired by persons performing oral sex on a male (i.e. fellatio) there are no cases of HIV which have been proven to be acquired from either receipt of unprotected oral sex or from cunnilingus.  Thus that you performed cunnilingus briefly on a CSW would not worry me that you acquired HIV.

Thus, I feel you have nothing to worry about.  If you wish to prove this to yourself, at this time a simple blood test for HIV (and syphilis) if you wish will prove that you were not infected.  In my opinion however, your risk is so low that there is little need for testing other than for reassurance.  I hope my comments will help to reassure you.  EWH