The operation is a big one with muscles cut, bits removed and heat used to seal up some areas on the inside where something was chopped off. Your op was only a few weeks ago and I think you will experience some discomfort for several weeks if not months to come especially when you move. I certainly did (mine was back in April/May) and in fact when I was at a classic car do just last weekend I experience a bit of a 'pull' when walking around the displays.
I think that with robotic surgery the outward signs, the entry ports, are so small and they heal up so quickly that it is difficult to relate them to what has gone on inside. This is far greater than you may think...in fact quite radical as the operation name suggests.
Keep taking the pills...it'll all get better in a few months. However, if you do feel the pain is a bit more than expected do get it checked out by your GP. A hernia is easy to come by at this stage and with only slight exertion. So, rest and recuperation are what are required....knock the weightlifting and canoeing on the head for a while http://community.prostatecanceruk.org/editors/tiny_mce/plugins/emoticons/img/smiley-wink.gif
Great results BTW...happy days,