I don't have the first clue how many steps I've been taking, but 5,000 sounds like an awful lot to me. Perhaps others are more qualified to comment.
As I understand it, the back of the knee is also quite traumatized by the surgery and is just as inflamed as the front of the knee. So swelling/tightness behind the knee is to be expected. I've been icing behind the knee more and more these days.