Your pain with flexion and in general (2) weeks after a total knee replacement is to be expected. I have had (2) total knee replacements (first RT knee 7/9/2020 & second LT knee 9/19/2020). I'm 75 years old. The physical therapy for the first (6-8) weeks after the surgery is really really very painful, but you have to just push through it, otherwise you'll end up with a stiff knee that requires the surgeon to manipulate it for you under general anesthesia. If your knee isn't so stiff that the physician wants to manipulate it himself, your knee will NOT become more flexible on it's own without physical therapy. And you don't want your PT to end before you can sufficiently flex your knee to the extent required. Without sufficient flexion in your knee, your gait will be affected and you won't be able to walk normally as you should, which will eventually become a big problem and cause new problems & new pain in the long run. The really bad pain, in my case, lasted until the end of the physical therapy (after the 12 weeks of therapy). I found that BEFORE the physical therapist worked on my knee, I had to take a pain medication dose. When the physical therapist first started working on bending & straightening my knee joint, I screamed in pain often, but she knew enough to not stop and kept working on my knee. At the end of the PT, your bending knee flexion should be 120 degrees or better and your straight leg flexion should be close to zero. As far as pain medications, get ahead of the pain. In other words, don't wait until the pain is so bad that you then HAVE to take a dose. Stay on schedule taking the pain medications, since it's better to not have the pain set in than it is to tamp it down after it becomes unbearable. I can now bend both knees 127 degrees and straighten both knees down to zero. Good luck.