two things jump out at me. One, if you take extra pain meds before PT, it is easy to injure yourself and not even know it. The pain meds mask any injury. I took my proscribed doses--with no extra before PT.
Second, was the line "Expand ROM"!! Does that mean the PT is pushing on your knee to get more rom? IF so, that is the problem right there. You cannot work to get more rom, it will happen once the swelling goes down. If someone is pushing and shoving your knee, they are CAUSING more swelling and pain and thus decreasing your rom.
Think of your knee as a garden hose, if it is filled with water, can you bend it? will bending break the hose? When the water is gone, the hose bends easily---just like your knee.
I never did anything outside of PT---no sets of 10 twice a day or anything else. I did make a point of walking my dogs every day---at least a little, and I do have an exercise bike. But, really most of the time, I was resting and elevating:
Elevating your leg to control swelling and pain
Using ice
It seems that your PT is the source of the level 8 pain---why not ask the PT office for a new one---a PT who has been trained within the last five years, when the thinking about rehabbing a TKR began to change. Yours is using the techniques of 10 years ago which have been found to be harmful.