Chronic bladder infection using a Gentamicin bladder wash

I have questions about the gentamycin bladder wash for a chronic bladder infection that will not go away. I'm not getting much information from the doctor. I need to know how long this bladder wash will work until the infection becomes immune to the antibiotic. I can't take any more oral or intravenous antibiotics. I've had C diff 3 times now. My stomach and intestines are a mess. I feel as if I live with food poisoning 24 hours a day because of the horrible gut pain and diarrhea and loose stools. Are there any other bladder wash that I can use when this Gentamycin doesn't work anymore. The doctor will NOT answer these questions. He say, "We'll cross that bridge when we get there". That doesn't cut it for me. I take care of my handicapped sister. She is totally dependent on me. There is no family to help us. I NEED to know if I have any options and what to expect. I am scared to say to much for fear the doctor will refuse to treat me. Is there anyone that has this same problem?