Hello,my Mom Had Dub With Menorrhagia,once Her Periods Were Over

hello,my mom had dub with menorrhagia,once her periods were over she was started on tab.meprate b.d for a month along with tab.sevista..she did not have her withdrawl bleed..she continues to take sevista twice a week since 23 oct,but has not got periods yet,her usg came back clear...what can be the reason for her amennorhea.