Burning sensation in penis but STD tests negative

[tfogel]

To provide some background info, I've been seeing a young lady for a couple of months now.  She is the first person with whom I have had sexual relations since ending a long term monogamous relationship.  She had unprotected sex with another man in June of this year, but before that she was also in a long term relationship.  She tested negative for STD's in July.    

About a week ago, I began experiencing a slight burning sensation in the tip of my penis especially after sex.  It has escalated now and slightly burns constantly, but especially after sex when it is particularly painful.  I experience no burning sensation while urinating nor do I have an urge to urinate more frequently.  

Today I was tested for NGU, Gonorrhea, Chlamydia, and Syphilis, and all tests came back negative.  

If I had a E Coli-based urinary tract infection, would that have shown up on the NGU test?  We recently engaged in anal sex, and I was wondering if that could be the cause of a urinary tract infection, but I'm wondering why this wouldn't have caused an increase in my white blood cell count that would have been detected in the STD tests I underwent today.

If this isn't a urinary tract infection, any thoughts on what else it could be given the negative STD test results?  Thank you in advance for your help.

[SINspg]

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