Sorry to hear about your problem. Tamoxifen
is not known to produce such side effects. Common side effects of tamoxifen include - hot flushes, endometrial hyperplasia
(for which regular pap smears need to be done), DVT, cataract
is unrelated to tamoxifen, but if you have received cyclophosphamide
in the past, it can be due to that drug, as it is known to cause cardiac side effects.
The weakness could either be due to some vascular event in the brain or brain mets and you should consult your oncologist
and rule these out.