nigella is more than likely right,
on a different note i had nsu, non specific ureatha, years ago, called by another std nowadays, anyway the doctor, who obviously was lacking in people skills, accused me or my wife of having an sleeping with someone else, i knew was not true on me behalf and as i had only been married a year or so, and worked with my wife and spent every hour with her, i guessed she had'nt either
so after a few strong words, the doctor backtracked and said it was also naturally occuring, i found out later it had been caused by small split in some scar tissue on my penis