It certainly doesn't sound like you are ready to return to work, so my vote is with your doctor. Fight hard to win that battle because once you start back it's difficult to say it's not working well and ask to stay home more. Work people tend to think you are "healed" and should be working at 100%. That won't be the case no matter when you go back, so the more time you have to really recover, the better.
I know it's tough, but do try not to compare yourself with anyone. Every recovery is unique to the individual and we must respect our bodies.....they know best! If it's telling you it needs a bit more time, then it does and there is no way to hurry up the healing process. Remember, this recovery is just a small portion of time when compared to the rest of your life with your new knee.