Leggs, those extra Oz's you drink go out-- also with the bowel, breathing, sweat, fluids in the eyes and nose. Not all fluids you drink end out the kidney and then the bladder.
Our bodies hold some fluid for good purposes too. Fluids "In and out" do not match up. Retention is noted with Urodynamics. Do you give yourself enough time to release more fluids?
I have urgency, frequency and hesitancy, but if I offer myself to sit every two hours the retained fluid drips out, but slowly. It's spasms of the bladder doing this to me. Worse when in relapse.
I just try to work with my plumbing or I would have to self-cath and would not like to start that if I don't have to. Good luck, I found the test a bit embarrassing, but that's me.