Jack,
Not sure 4 weeks seems a little long to have any major pain. How big was the superficial tumor? What stage/grade? I did have a recurrance of henaturia (blood in urine) about 4 weeks after my TURB, however that was during BCG therapy. You urologist should be able to address your concerns, but the contant thirst/diarrhea does not sound like a bladder cancer problem?
On the flip side I just had my 3 month checkup without a recurrance. Not a whole lot you can do to prevent a recurrance, but just remain vigilant in your checkups... If your recurrances get real bad, they may try BCG.