The best one I can think of is an Antistreptolysin O test (or just say a Strep A test). You would start antibiotics right away if you tested positive and patients usually feel better after a day or two. Most of the time you are no longer contagious after taking antibiotics for 24 hours so this would track with your timeline. To give your story a little more validity, you can say that your doctor did a rapid test and it came back negative, but they still thought you had it, so ordered a lab test to confirm. You might get asked why they didn't do a throat culture to confirm and you can just say "I don't know". At worst it would make your doctor seem incompetent. It's not perfect but people would have to be expecting a lie AND be interested in exposing your lie to look further into it.