I did genetic testing which was funded as I had my mother and aunt who both had breast cancer. It was negative. They take extensive family history and a blood test. I chose to do it not only for myself but the implications on my sister's and nieces if it were positive. Also an advantage is that they keep in touch annually and if there are any new genes identified for breast cancer they notify you if it affects you.
I have also taken Tamoxifen for 18 months now. Side effects mainly were hot flushes and dry skin and some mood swings. . Side effects seemed to settle after the first year..
Good luck to you