Ask your doctor if he/she could get you a CPM machine to use. You need to be doing all the recommended exercises!
Come on give it a chance, and give yourself a chance as well, 3 weeks is not a long to get it back together yet is it, just how long was you told it would be to you get full movement?
Good Luck
Are you still in therapy? It is still early in your recovery and doing the PT and all of the home exercises will get more range of motion in your knee. I know from experience. Good luck!!