Hi GD
Im no expert in side effects of your surgery but I know a bit about Babies and nappy rash!
Urine, being acidic, does cause a lot of soreness if it stays in contact with the skin for any length of time. Havng to wear pads makes the potential for this so much greater. Inerestingly enough if you wash too frequntly, too hard or with too much soap it actually removes the antibodies that naturally try to combat the irritation. I am only guessing here but it might be worth trying a thin coating of Sudocrem after washing, you can get it over the counter in most chemists and supermarkets quite cheaply. Also you can reduce the acid level in your urine by having a teaspoon of bicarbonate of soda dissoved in water and drunk at night time.
If this doesn't ease the soreness and the rash in 48 hours then maybe ask your GP or clinicl nurse specialist. If you have any worse things like discharge or bleeding then don't hesitate go to them first.
I hope your progress post surgery is continuing well other than this.?
Best wishes
xx
Mo