Welcome, @gor. The temptation to worry about any unusual sign or symptom possibly indicating that breast cancer is back. It's every cancer survivor's biggest fear. In fact, @sclark3 just posted earlier today about feeling off - a strong gut feeling that something's not right. As I said to her, you know your body better than anyone. If something isn't right, it's time to get a professional opinion.

The first thing to do is to make an appointment as soon as possible with your primary care physician. They will do tests and rule out all possible causes. If they suspect possible return of cancer, they will refer you back to your cancer team.

In my non-medical opinion, I wonder if you might be experiencing shingles, @gor. Here's some information about shingles from Mayo Clinic.
https://www.mayoclinic.org/diseases-conditions/shingles/symptoms-causes/syc-20353054
Does this sound like what you are experiencing?