penis still burning 9 days after flagyl and zithromax treatment

[manneedinghelp]

I began experiencing burning in my penis roughly a month ago.  The symptoms subsided, but then returned strongly again last week.  Notably, I have not had any discharge.  I went to an STD clinic 9 days ago (the day after the symptoms recurred, following sex), where I tested negative for gonorrhea.  They also took tests for chlamydia and syphilis (not related to the burning, but their general policy), which still haven't been come back yet.  They went ahead and gave me single-dose blasts of metronidazole (aka flagyl) for the possibility of trichomoniasis, and azithromycin for the possibility of chlamydia.  Everything I've been advised and read says those should have cleared up the symptoms with 7 days.  But it's now been 9 days, and the burning persists.  What could this mean?  Could I have not received a strong enough dose, and need more (I weigh 225 pounds)?  Or could there be a non-STD cause for this?  Uuggghhh . . .  I want this -- and my abstinence -- to stop!  Thanks so much for any help.

[manneedinghelp]

Update:  the tests for chlamydia and syphilis came back negative, and the negative gonorrhea result was confirmed by the urine test (already tested negative for that via the swab).  The burning sensation is persisting, however, although it is not as strong as it was.  And again, there has never been any discharge.  This is now a full two weeks after treatment.  Do any medical professionals read this board, who might be able to provide some insight?  Recommendation for next step(s)?  For privacy reasons, I'm reluctant to go to my primary physician.  Please help!  Thanks.

[MoonBear33]

There could be a non-STD cause... the question is, can modern medicine identify it? Anything they can't identify they file under "Non-infectious Chronic Prostatits" or similar names. I have, since 4 years ago, a "Non-infectious Chronic Prostatits" that causes light-medium burning from the bladder to the urethra with no discharge for periods of 1 week to 1 month, then vanishes for some time and returns again. All tests were negative, normal PSA, normal bladder and prostate ecograhy, all cultures negative. The possibilities the urologists give me are:
- Uncommon/Rare Herpes outbreaks either inside the urethra ou bladder or even in the prostate
- Uncommon/Rare bacterial infection that cannot be cultured and is resistant to all known antibiotics (in these 4 years i have taken all types of antibiotics know to man, even gen 3 cephalosporin that is used for antibiotics resistant bacteria)
- Viral infection by some virus that cannot be detected
- Physical causes. Either the position or shape of my prostate is affected by another organ/muscle and it causes the prostate to respond with inflamation and the inflamation causes the symptoms.
My symptoms are stronger at night and usually disappear/become very light after lying down for 30min. The burning also vanishes completely while urinating.
An ice pack helps me a lot at night when i'm having one of these "crisis" (10min on, 20min off, repeat).
Sadly when tests are negatives, doctors become as clueless as we are. :(