Risk of me getting herpes from oral sex?

i had unprotected oral sex but a protected vaginal sex from a prostitute in a legal geylang (singapore) house 12 days ago. i had blood check yesterday at the clinic and my result for both hiv and syphills came out negative which is a very good news for me. tdy was fine then i came back home late afternoon tdy and saw i had a clear watery blister on my penis head (not sure is it really a watery blister or i was just to worried and thinking).. my penis head hurts for abt 4-5 days now. is their a high risk for me getting herpes or what are other possible diesases? pls help me! thank you