Hello. Thank you for writing to us at healthcaremagic
Unprotected Oral sex with a commercial sex worker (csw) is a risk factor for STD's 
Receptive Oral sex can transmit 
gonorrhea, chlamydia, syphilis and herpes. HIV is a risk if the partner giving oral sex has oral sores, which increases the risk.e.g if an HIV positive sexual partner has active sores of oro-labial herpes at the time of sexual act, then not only is there increased risk for 
genital herpes but also HIV.
I suggest you to visit a sexual health specialist for 
counselling and also get yourself tested at appropriate intervals for STD's
Testing for gonorrhea or chlamydia is easy. A swab test for detecting microbial DNA can be done at 2 weeks post sexual contact.
Herpes can be detected earliest at 2 weeks with a 
blood test for Hsv type 1 &2 by ELISA.
Screening for HIV and syphilis can be done earliest at 1 month and to be repeated later at 3 months for a conclusive result.
Regards