Estrogen helps regulate our body's temperature so when your estrogen levels are reduced (menopause, chemotherapy, tamoxifen, arimidex etc) the body struggles with maintaining an even temperature and we have hot flushes or chills or both.
A lack of estrogen also causes joint, muscle and bone pain (fabulous hey!) so it sounds like you are experiencing a drop in your estrogen levels which is very important if you are ER+ .
Something that worked for me with dealing with hot flushes is to visualise cancer cells being burnt up in flames. This does not actually happen but the imagery worked for me and I have got to the point where I accept hot flushes with a smile - well maybe it's a bit of a grimace but I know that the hot flushes are a symptom of low estrogen and I know that low estrogen will help reduce my risk of recurrence so that somehow makes me feel better about it all.
If anyone has any ideas about how to mentally deal with joint pain I'm all ears!