Oh dear sorry to hear the problems are still on going. Must admit when I read your earlier post I thought of trapped nerve in his back  Usually leg problems and inability to pass urine, usually combined with constipation of sudden onset are due to this so it will be helpful to have the MRI scan done. (painkillers will probably cause constipation anyway). If nothing shows up there you still have the urology appointment to at least sort the bladder out.
Regarding painkillers  if the paracetamol are ineffective ask them to prescribe something stronger maybe with an anti inflamatory base (if he doesn't have any other condition which contra indicates these)
In hospitals now they all have this pain scoring system so they can look back on that and see that his pain hasn't been well controlled and prescribe something else.
I hope he gets some relief soon and they sort the problem out quickly.
Carole
x