Betadine would seem to take the body off its usual self-cleansing track, and so would the antibiotics you took (though they obviously worked to heal the
infection, your normal
urinary-
tract environment got disrupted). You need something gentler and more close to natural, since the area is disrupted and irritated. Also, if you haven't, you might change to washing your underwear in one of the laundry soaps made for washing babies' things, such as Dreft.