Follow up with your Dr for more testing, your negative tests and your treatment rule out a STD. Not sure exactly what it could be but my guess would be fungial in nature.
I am experiencing something similar and believe it could be caused by mycoplasma genitalium or ureaplasma, two STD's not tested for during the regular screening. These require special tests not covered by medical but it's certainly worth looking into in order to have yourself and wife treated as they can cUss complications particularly in women.
Btw, did yo originally test positive for either gonorrhea or chlamydia? Or did you always test negative but the your GP gave you the empirical treatment for your symptoms?
just treated the symptoms with two seperate meds can't remember the name but it was for 10 days twice