I Am Under Going Chemotherapy/radiation Of The Anus And I

I am under going chemotherapy/radiation of the Anus and I have terrible urgency to urinate. I mean I can't drive for more than 20 minutes and I have to pull into a parking lot and drop my drawers and pee in a gator aide bottle! The pain of urinating is horrific! I have to drink a lot of fluids so I don't dehydrate but I hate to drink so much because I know I will have to pee! My GP put me on 1,000 MG of Ciprofloxin. The urine sample came back with no growth. I believe my radiologist is burning up my bladder but he says NO. I know better because he gave me his home site to go to and it is there! HELP!!