Hello. I worked in an inpatient unit on the ortho floor at the university of Iowa hospitals and clinics. We took care of many joint replacement patients. This is what I know:

Knee replacements really hurt. The rehab is pretty extensive. You should expect to feel a good deal of pain for at the very least the first 6 weeks. When you stop to think about what your surgeon really did for you, it was very extensive. He had to pull out your old knee, move a lot of muscle tissue and tendons, then he had to scrape out any left over debris, then screw into your leg your new knee joint. All of that moving around can really cause pain. You stated that your knee is very stiff. Have you been using a CPM machine (continuous passive motion)? These help to restore function and flexibility to your knee. Are you attending physical therapy? This is also very helpful in getting your knee to move. Ulltimately, it takes about 3 months before you really feel like your old self. If you are able to get around with just a cane at three weeks, then you are doing great! If you have further concerns, if the incision becomes very red, hot, or if there is an increase in drainage from the knee, contact your physician right away. You don't want complications.