Not all women have hot flashes with tamoxifen, but most do to some degree. The drug is working regardless of side effeects. It just means that you are fortunate to not have lots of hot flashes (mine are not often or bad.)
I hope that you're one of the lucky ones!
There is no way to tell what side effects will be experienced by an indivudual ... whether or not you are effected means nothing except of course if you don't have the side effects, you can consider yourself very fortunate. All the Chemo, etc. drugs have several side effects but not everyone will experience the same ones OR to the same degree. Regards ....