I am still laughing at the feces!!! Never ask a nurse for help if you are not prepared for the worst!!
I do think that I Personally was further along at 3 months, but if you are not, then that is that. If you feel that you are not where you want to be at 16 weeks, it is time for a second opinion. There are many reasons for a knee to remain painful after a tkr.
Those questions are best answered by someone who is used to dealing with Tkr's that have not settled down to be nice, new knees. Usually if the doctor lists that he does revisions in his bio, that might be a person you would want to see.