Knees, shoulders, hips and ankles are all "large joints and typically aren't the presenting signs of RA. My impression of RA is disfigured hands.
https://www.mayoclinic.org/diseases-conditions/rheumatoid-arthritis/symptoms-causes/syc-20353648
"Early rheumatoid arthritis tends to affect your smaller joints first — particularly the joints that attach your fingers to your hands and your toes to your feet.

As the disease progresses, symptoms often spread to the wrists, knees, ankles, elbows, hips and shoulders. In most cases, symptoms occur in the same joints on both sides of your body."

The way you describe the onset of symptoms sounds eerily like reactive arthritis to me. You don't have to be aware of any infection to have reactive arthritis. Often the infection is long gone by the time symptoms of reactive arthritis begin.

Were you ever tested for HLA-B27? A positive result would not be definitive of anything but it might be useful information.
https://www.ncbi.nlm.nih.gov/books/NBK551523/
You only need to have the HLA-B27 test once. I don't think doctors like to request this test because it is probably expensive. Also, there isn't anything they can do about it if your HLA-B27 is positive. Being HLA-B27 positive won't prevent you from being diagnosed with something else like RA or PMR later on.

PMR is more of a syndrome rather than an exact diagnosis. My understanding of PMR is that it is more of a conglomeration of many things which isn't well defined. I think doctors call things PMR and throw Prednisone at the problem. When people have a rapid response to prednisone it is like confirmation of PMR. However, a rapid response to Prednisone doesn't confirm anything either.