Hi. I had my da Vinci op at the end of April and my experience with the catheter was exactly you describe. Painful and uncomfortable with serious spasms, heavy bypassing and painful when sitting on the loo.
I contacted my nursing team and the helpful call centre at Prostate cancer UK. Each time I was told that these symptoms were 'normal' as it is the bladder trying to 'reject' the catheter as it's a foreign object inside the bladder.
I must say it wasn't a pleasant experience but over the 2 weeks I had the catheter in things didn't improve very much BUT the light at the end of the tunnel is that once the twoc is done and the catheter comes out, all this will go away immediately.
So sorry for not coming up with a resolution for you, but I found that over the time it was in, I got more used to the discomfort but I hope you can take some solace in that this will be gone very soon.