If you need to take prescription pain meds, then take them. There is no prize for suffering in pain, and by avoiding pain meds when needed, you can actually retard the body's healing process. Any nurse will tell you that. The short time you will probably need you isn't going to cause most people any if much constipation problem. Pain is a very personal and subjective thing, and only you will know how you are feeling after you are released from the hospital.
All the advice about drinking lots of water is very important. Got to keep flushing out your system, even if you don't feel like it. It will make your hopefully short catheter time go easier on you. If your lifestyle allows, its easier to keep the big catheter bag on most of the time, the "night" bag, typically holds 2000 ml, some as much as 4000ml. If you do use the leg bag, they typically hold around 400 ml. You don't want to lie down with a leg bag on, as it can force urine back up the catheter into you bladder. Urine is only sterile in your bladder.
Walking is great, if you are up to it, try the best you can every day.
David in SC
Age: 58, 56 dx, PSA: 7/07 5.8, 10/08 16.3
3rd Biopsy: 9/08 7 of 7 Positive, 40-90%, Gleason 4+3
open RP: 11/08, on catheters for 101 days
Path Rpt: Gleason 3+4, pT2c, 42g, 20% cancer, 1 pos margin
Incont & ED: None
Post Surgery PSA: 2/09 .05,5/09 .1, 6/09 .11. 8/09 .16
Post SRT PSA: 1/10 .12, 4/8 .04, 8/6 .06, 2/11 1.24, 4/11 3.81
Latest: 6 Corr Surgeries to Bladder Neck, SP Catheter since 10/1/9, SRT 39 Sess/72 gy ended 11/09, 21 Catheters, Ileal Conduit Surgery 9/10