Perhaps, you have a persistent/resistant type of bacteria and need
to treat it for a long time with a combination of
antibiotics, or with stronger antibiotics that you've already had.
Aside from the scope, did you ever have any other tests, like an ultrasound (kidneys, ureters etc.) to check if there are any anatomical defects or kidney stones that could be causing the frequent UTI's?
You mentioned you suffer from candida albicans. That's a yeast infection. Are you treating it?