56p, I think it is easy to look at the rather small scars on your tummy and think you should already have recovered. Taking out the prostate is major surgery, and your body has suffered severe trauma. Being short of stamina is perfectly normal, but if you slowly build up strength as suggested by Chris and Francij you will gradually be capable of more.
We are all different, but in my case it took 6 weeks before I felt I actually was going to be able to return to the level of activity I was used to.