Pain and nodule on ribs

I had a double mastectomy to flat closure in June 2024 due to bilateral breast cancer (IDC grade 3 and IDL grade 2). No rads or chemo, and haven't taken tamoxifen. Lately, I have developed a hard nodule on my left ribs (on two ribs directly above the other along my scar line). They feel bony, but they are new, and it scared me. I first saw it through a tank top I was wearing. I am also having pain in my ribs on both sides, and the left ones look more sunken than they did previously, where the breast once was. The doctor ordered X-rays (came back fine) and has referred me to the breast centre for an ultrasound, but the wait is a month long. Curious if anyone else has had these things happen 18 months post mastectomy? Obviously, I am pretty worried about a recurrence.