For a time, I have been noticing a colourless, odourless,

For a long time, I have been noticing a colourless, odourless, sticky liquid coming out of my penis whenever I squeeze/milk it, especially before the first morning urine. I recently got worried about this and went for a std panel test (I have had one episode of unprotected oral sex - receiving only - about one year back, and numerous handjobs at massage parlours in recent past). The tests included blood tests for chlamydia, gonorrhea, HIV, hepatitis B, herpes; urethral swab for gonorrhea; and urine bacterial culture, gonorrhoea culture, mycoplasma culture and ureaplasma culture. All tests came back completely normal, except for the gram stain of the urethral swab which said "no gram-negative bacilli found, many pus cells seen).
The doctor - an STD specialist - suspects I have had gonorrhea, though he is not entirely sure. He administered me one antibiotics injection and asked me to take a single-dose of 4 antibiotic tablets which I did.
My questions are:
(a) Do you agree with my doctor that this is most likely gonorrhea (despite the fact that the gram stain of the urethral swab and the urine culture for gonorrhea returned normal results.)
(b) Could it be simply a UTI (and not an STD)? Perhaps my doctor is over-reacting?
(c) Could it be an NSU caused by non-sexual means?
(d) Apart from one incident of unprotected oral sex, I have only had handjobs; absolutely no vaginal or anal sex with anyone except my loyal wife over the last 10 years. What is the likelihood of my contracting an STD through the exposures I have had?