I am not sure about the length of time, but I had recurring UTI's for about 6 years after my colon and bladder grew together and exchanged contents severely. Then I read an article about what is called biofilm. Apparently, some bacteria will create a film over them that keeps antibiotics from reaching them, i.e. biofilm. Once the coast is deemed to be clear they come out. The only way to get rid of them is to treat them with one type of antibiotic for several days, then switch to a different type of antibiotic. Once I told the doctor this, he was aware and started me on this regiment. It worked.

I have the same, can't get rid of UTI which put me in hospital with sepsis in November due to no symptoms leading up to total loss of ability to do anything. I am now on my third antibiotic in a row (I test at home with same strips the doctors use, from online) and am considering trying Methanemine one a day, or fosamin once a week. (sp) They have been successful for others on this blog. Macrobid didn't help me several times over the past year. I am now on cephalex 500 mg 2xday. Appointment Thursday for discussing my above options. Good luck but count on a long period of final diagnosis.