Good morning -
I think I will bring @artscaping into this discussion. She has had swelling like yours, determined to be a cyst, but it can also be from the healing process. There are a few techniques you can try to encourage the fluid to drain without a needle, and I am sure she can describe them to you.
I am glad your surgeon is cautious about introducing a needle into your new knee - the last thing you want is an infection!
Sue