I can understand your frustrations and concerns as I have experienced all of what you are experiencing now. I had my right knee replaced at age 19 because of a genetic disability that left my right knee with end-stage arthritis beginning at the age of 9. I had a horrid recovery and also had two manipulations because my scar tissue growth was so aggressive. My range-of-motion was 10-40 degrees for the better part of the first year.
I kept with my rehab and stayed active, and eventually I felt a “pop” in my knee and over the next few days I went to 0-100 degree flexion and extension. This all developed 1.5-2 years after my initial replacement. I can say 11 years later, my knee has not degraded at all and my quality of life is so much better. Stick with it, it will come, even if it takes longer than what others maybe expected. Stick with the PT & keep your spirits up.
@maggiet, how are your exercises going? I admit that I did not push myself hard enough because of the pain and that hindered my progress. How is your pain?