[Forsyth]

Suggestion if all else fail.

Take MRI scans of pelvic and groin areas(Will probably cost quite a bit)

Purpose : To check for any abnormalities eg a growth(there's a medical term for it, can't recall it for now).
The infection maybe in the growth, protected from medication(will need biopsy to confirm).
However, when you have sex, body movement causes pressure on the growth, and the infection leaks out.

There is a very very very very low possibility of this.
You should consult a doctor regarding the validity of this theory.
But as I said, if all else fails.

If I were in your shoes, I would go for a strict regiment of exercise and correct diet for 6mths before dipping my feet in the water again.
And if I still have it, I would then consider the MRI scans.

Peace.