Oral sex isn't completely free of STD risk, but it's a lot safer than unprotected anal or vaginal sex. Still, your symptoms could be due to urethritis acquired during that exposure, but your symptoms are atypical because the pain is not notable during urination, plus absence of discharge. You imply you're concerned about herpes, but that's unlikely:  initial genital herpes usually includes external herpetic lesions, not urethritis alone; and with herpetic urethritis the urethral burning is a whole not worse than you describe, and typically is excrutiating during urination. 

Gonorrhea? Possible from oral sex, but within 3-4 days almost always causes overt pus dripping from the penis and quite painful urination. Chlamydia? Extremely unlikely -- rarely infects the throat and thus rarely acquired by oral sex. OTOH, not impossible -- and chlamydial urethritis can be associated with very mild symptoms. What about a non STD urinary tract infection? Your symptoms sort of fit -- the bladder fullness and perhaps enhanced sense of needing to urinate when it's time to go. However, not likely acquired by oral sex. (UTI is fairly common in men who are the insertive partners in anal sex, but not from oral.) Finally, it is conceivable you have nongonococcal urethritis (NGU), which can follow oral sex. Here too, your symptoms are atypical for the reasons noted above. But when NGU follows oral sex, it is believed to often result from exposure to entirely normal oral bacteria and to be harmless.

What to do now? For now, probably you can safely do nothing and see how your symptoms evolve over a few more days. Keep an eye out for scant discharge, which might show up only as a bit of underwear staining, or crusting around the opening when you haven't urinated for several hours (like on awakening in the morning). If no discharge and the burning fades away, I would suggest nothing more. If you develop discharge or if no change as the weekend approaches, see a doctor (preferably one familiar with STDs), and have a urine gonorrhea and chlamydia test, to exclude the slim possibilty of either of them.

In the meantime, stay mellow. Most likely nothing is wrong, and almost certainly nothing serious or that will cause complications with a few days delay in diagnosis and possible treatment.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD