Stinging/Burning In Penis - Worse After Ejaculation

[pony89]

Several months ago I started getting a burning or stinging feeling in the opening of my urethra (circumcised).  If anyone has ever accidentally got some soap in there, this is what it feels like.  At first it seemed to be there all the time but since then it has come and gone.  It definitely gets worse post-ejaculation.  Sometimes it will last a couple of hours and other times it can be days.  It makes doing almost anything uncomfortable because any movement or walking causes the tip to rub on underwear and it hurts.

I've been to a few different doctors.  I've been tested for all STDs and negative.  Treated with oral and injected antibiotics just in case.  I've had a prostate exam, prostate ultrasound, pelvic CT, cystoscopy, full urine and blood work ups.  They have found nothing.  

So what is left here guys?  I am thinking that there are only two options.  One, there is something coming out of the prostate that is burning the urethral opening.  Perhaps a lingering infection?  I read that an infection in the prostate can be difficult to kill due to lack of blood flow to the area.  Or two, there is something wrong with the urethra itself that is causing it to be irritated.  I was wondering if it could be some sort of fungal infection but every doctor I mention that to immediately dismisses it.  I was also recently given a prescription for topical antifungal for jock itch.  This is why I am wondering if there is something yeast/fungal related going on.  Perhaps a more systemic infection.  If that is true, then it is my understanding that the antibiotics would make it worse.

Any thoughts/ideas/advice would be greatly appreciated.  I am running out of things to check for here.  

Thanks.