Oral sex is amongst the lowest risk penetrative sexual encounters.  There are no proven cases in which someone has acquired HIV from receipt of oral sex from an untreated, infected person and the risk of acquiring HIV from performing oral sex on a n untreated person with HIV is very, very low- less than 1 infection per more than 10,000 exposures (I.e. less than 1 100th of 1%).  In the case you describe, unless you know otherwise, it is unlikely that your partner had HIV or that if he did, that you acquired the infection.  If you wish to rule out infection, you could test at this time.  Results 5 weeks after an exposure are virtually conclusive ( more than 99%) and at 6 weeks results would be entirely conclusive.  

I hope that this information is helpful.  If I were you I would not be worried.  EWH