Make sure you get enough sleep, too. Your body does an enormous amount of repair work just on an everyday basis while you're sleeping. When you're recovering from an injury, you may need quite a bit more than you normally would. I'm a runner, and when I was dealing with a stress fracture in my ankle, I was sleeping a full extra hour every night.
I hope your spirits lift soon. *hugs* Keep up with your PT, and I agree with the suggestion to get in the pool. Your knee will bear less weight when you're in the water so you can work on range of motion and not have to worry as much about it holding you up at the same time.