I spent my entire professional life in health care, but only learned of this during my prostate journey: My urologist said that as we get older, our bladders get "smaller." So, if you are 60 "+" years old, your bladder doesn't hold what it used to, and...the prostate provided "physical support" to your bladder. It sat under your bladder like a little base unit. But now it is gone, and your bladder no longer has tat extra support. And of course, the most important of your two sphincters that control urination was removed with the prostate. Your body is learning to control urine retention with the one remaining, weaker/secondary sphincter. Also...
If you haven't received such an order, ask your urologist for 8 sessions of Pelvic Floor Physical Therapy (PFPT). Most insurance companies pay for it...usually initially, approving just 2-3 sessions, but all it takes (per my PFPT therapist), is for the therapist to submit the need/request for additional sessions to your insurance company which should be approved. I was approved for two sessions, and after submission for more, I was approved for eight sessions. There are MANY more pelvic floor exercises than the basic Kegel exercises...all very similar to strengthen and control those small pelvic floor muscles, but the therapy does help. Part of that therapy will include a conscious modification of your consumption of liquids. I never even thought about how much I drink, what I drink, and the frequency of drinking. My/your PFPT therapist will tell you to make absolutely sure that you urinate very two hours whether you think you need to or not, and to only consume "8" ounces of liquid at a time. That has been the hardest for me since so many drinks are bottled/canned in 12 oz sizes. I discovered the 8 ounce mini size sodas as a result. My therapist also said it is best to consume the 8 ounces immediately after you urinate...but only if you are thirsty. She also laid down an absolute rule for my first 6-12 months post-op: No caffeine, no acidic beverages like O.J. and other juices that tend to be acidic, and try to avoid carbonation as well. Carbonated drinks ultimately become acidic in your body, and of course, if you read the label, almost all contain citric acid, phosphoric acid, etc. Those are all bladder irritants, and your bladder is kind of "angry" right now having lost some physical support to support the urine. The surgical trauma left your bladder kind of "pissed off" (pun intended) and angry...it is in recovery mode, so be kind to it. The retraining to drink only 8 ounces was easier than I thought. I am almost 8 months post-op now, and I am slowly re-introducing orange juice to my liquid consumption, as well as my 8 ounce 7-Up Zero, Fresca, Diet Decaf Coke, etc., all with no caffeine. Good luck with it, but you have a ways to go. Lastly, I wouldn't drink anything after dinner, and of course, urinate before you go to bed. Being flat/prone on your back while you sleep, should help alleviate any gravitational influence on your bladder while you sleep. Even now, I still get up between 4:30 - 6:00 a.m. to urinate, especially if I went to bed between 10:00 - 11:00 p.m., instead of, say, midnight. I don't have great urgency...I am actually just starting to wake up, and realize: "hmm, I guess I should get up to urinate...I kind of feel like I could/should." Everyone is different though. The good news is that you will regain continence. Good luck.