You are right to be concerned and to seek immediate action. Your knee has some of the signs of infection and "wait and see" is not a good approach.
Since you mentioned you have seen an infectious disease doctor before about another issue, I suggest your first step is to arrange an appointment with him on an emergency basis. When you call the office to schedule, tell them you believe your TKR is infected and, if possible, send them these photos. The fact that this "bubble" that appears to contain pus has appeared since Thursday, is significant.
Go ahead with the aspiration on Monday. That is typically one of the first steps when an infection is suspected and it should yield some answers about that possibility. If the doctor didn't order blood tests for you, ask if you can have test for elevated serum erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) concentration as well as elevated synovial white blood cell (WBC) count. These are necessary along with the aspiration to determine if an infection might be present. Normally, the aspiration and blood work would be done right away and I'm not sure why there was this delay, but it shouldn't be a problem. It may take a few days to get the results from the tests of the fluid drawn and know exactly what you're dealing with. The blood results should be faster.
Periprosthetic infections can occur for a number of reasons and not all are completely understood. There doesn't have to be an external cause such as an injury or other means for bacteria to enter your body. Even though everything is considered surgically sterile when your implant is placed, there is the possibility of bacteria on the implant itself encased in a protective biofilm. It can remain there dormant for extended periods of time until something triggers it to activate.
Here is a pretty comprehensive thread on the subject from our BoneSmart Library.
Infection: peri-prosthetic infection - also known as late onset infection
Here are some surgeons for you to explore. You are fortunate to be in an area where there are many possibilities. My recommendation would be to go to one of the surgeons connected with the Hospital for Special Surgery (HSS). I am personally familiar with Dr. Della Valle, but others on the staff there would be equally good.
New York City
Hospital for Special Surgery (HSS)
Stavros Niarchos Foundation Complex Joint Reconstruction Center
is a special program created with a $10M grant that deals with diagnosing and treating the most challenging knee and hip replacement problems. As part of the diagnosis, a committee of surgeons meets to discuss your case. There is a fee for your case review. This center is headed up by Dr.Thomas Sculco.
Revision surgeons at Hospital for Special Surgery, New York City
(revisions of both hip and knee):
Dr. Goeffrey Westrich
Dr. Russell Windsor
Dr. Seth Jerabek
- recommended by Skybig. Working with him on severe metal allergy (Nickel, Chromium, Molybdenum, Vanadium and Aluminum and Zirconium sensitivity).
Dr. Michael Cross
Dr. Michael Parks
New York City
Hospital for Special Surgery (HHS) surgeons for knee revisions:
- Speaker at 2018 ICJR workshop on problem hips and knees
Dr. Della Valle
(I have heard several recommendations on this surgeon)
Dr. Jose Rodriguez
(primary hip recommendation, but does knees as well)
(primary hip recommendation, does knees as well but doesn't take Medicare)
New York City area
Dr. James Nicholson
14 Tech Drive, #11
East Setauket, NY 11733
Dr. Bradley Gerber
36 Lincoln Avenue
Rockville Center, New York 11570
Please let us know how things go with your knee. I will be looking forward to your updates. Thanks so much for the photos. That really helps determine the urgency of your situation.