I had the same problem for 3 months . For 2 treatments it was for 5 days. The last time the Dr prescribed 10 days of the same antibiotic ( that has always worked for me).
I understand the fear of having anti-biotics not work and I am 75, but also it seems to me that 5 days is not always enough for stubborn infections.
I have heard of being on low dose of antibiotics for several months, but not known anyone that has done that.