@KimF
Letrozole side effects may vary widely, so it can be hard to tell if you are not having any or if they are delayed. Certainly 10 days are very early days indeed. From the vantage point of nearly 10 years of Letrozole (I stop in May, hooray) I have never had joint pain, aches or menopausal type symptoms, which can occur. My bone density has taken a bit of a bashing but that is symptom-less (unless I fall and break something!). My bone density was excellent when I started and also my age is a contributing factor over a decade. It’s worth having a bone density test to know what’s what. I have vaginal dryness, which can and has been treated. You may have relatively few side effects.
I was 67 when diagnosed so my estrogen levels were probably not high and will have fallen steadily since. Worth remembering if you need estrogen treatment for vaginal dryness. Best wishes.