Hello. Welcome to hcm.
Most common cause for no periods after surgery is due to symmonds disease. Here due to excessive blood loss,there wil be clot in pituitary. As you have not mentioned about surgery,if there is obstruction to passage of mentrual blood also can cause loss of menstruation
I advice you to under ct scan
brain and also ultra sound
abdomen. Harmone study will help to identify the cause. Taking drugs with out a proper diagnosis is of no help.
All the best