Welcome to the forum. Your question has some parallels with the one immediately preceding it. Please read it so I don't have to repeat some basic facts about NGU following oral sex:
http://www.medhelp.org/posts/STDs/confused-about-ngu/show/1560405
Unlike the other questioner, it is apparent you did indeed have NGU following your exposure last October and the problem cleared up with antibiotics. Recurrent NGU is quite a common problem, but generally that happens within a few weeks, and your current symptoms probably are unrelated to the previous episode or that sexual exposure. As you found first time, NGU generally causes discharge as well as painful urination -- so if no discharge develops this time, that also would argue against recurrent NGU.
However, you are correct that herpes could be responsible -- unlikely but should be checked out. HSV is responsible for a small minority of NGU cases (under 5%), and HSV-1 can be acquired by oral sex. However, herpetic NGU usually is more painful than your description implies. Still, it is possible that your current symptoms are due to a herpes recurrence. I recommend you return to your doctor and discuss testing for HSV. Do it very soon; reliable testing has to be done within a few days of onset. Herpes NGU clears up on its own in a few days; it might be that the improvement while taking antibiotic was coincidental, not due to the antibotic treatment.
Those comments respond to questions 2 adn 3. Question 1: There is no lab test for NGU. The diagnosis is based on careful examination to look for abnormal discharge or other abnormalities, like redness of the urethral opening; and to examine a swab specimen under a microscope for elevated white blood cells. If no WBC are seen, it is strong evidence against NGU.
Let me emphasize that herpes probably is not the problem. But careful examination and lab testing are the only way to know. I'll be happy to comment further if you want to report back with the results of professional evaluation.
Regards-- HHH, MD