Robin, the fact that your knee is swelling when you get up and "do a few things" is telling you that you need to stop trying to do those activities - whatever "a few things" might be. If you've been pushing yourself like this throughout your recovery, you're keeping your knee in a constant state of irritation. Sitting down for 15 minutes does little good. If you have pain and swelling, you need to be icing and elevating most of the day for several weeks to see improvement. This whole process takes time. For some folks, it takes more than they imagined.
The redness and soreness in your knee is most likely due to the near fall you had. You'll need to give that at least a couple of weeks to get better.
One of the other members suggested you try and focus on the things that are better since your surgery. That would be wise. When you constantly dwell on the things you can't do, it's bound to make you feel worse. I also suggest that you may not be getting enough rest. Try napping during the day. And also try taking something for any pain you're having. Doses of 1000mg of Tylenol can help with low grade to moderate pain. Stiffness is a form of pain, so I know you have it. You can take up to 4000mg of Tylenol in a 24 hour period (just be sure to count any other medications you may take that have acetaminophen in them in that total). Pain (even at a low level) can wear a person down mentally and physically. Please don't let yourself fall into that trap.