I feel I have to reply to this as I was going through the same thing. II had chemo, radiation and a lumpectomy all from December of 2018 and rang the bell in December of 2019. I started the Anestrozole (1mg) at the beginning of December 2019. In February of 2020 I had a colonoscopy and was given a 7 day course of Cipro. Within four days of taking Cipro I developed severe pain in my muscles and joints. I was told that if it was the Cipro the pain would stop once I finished it. It did not. I spoke to the oncologist and he took me off the Anestrozole for two weeks. However, the pain persisted. To make a long story short, after seeing my regular GP, the radiologist and then a neurologist, it was discovered through blood work that I had PMR (polymyalgia Rheumatica). He sent me to a rheumatologist who put me on Prednisone and Voila! Pain gone. However it took months to discover this. No one knows how the symptoms start nor does there seem to be a "cure" for it. I have had no problems with the Anestrozole and have been taking it for over a year now. I am 78. Just to let you know that there might be other reasons for the pains rather than the Anestrozole. Good luck.