My sister after 3 months delivery had heavy menstral bleeding for 1 month, now for 3 months no regular periods. Is this normal, medicine is needed.?

Common. . She may have polycystic ovarian syndrome (PCOS). This leads to irregular and missed periods. If she had significant bleeding at the time of the pregnancy to the point they needed to do a scraping of her uterus for or a transfusion she may have another type of endocrine deficiency syndrome though I would expect this to be very unlikely. Being on birth control pills or ring may be beneficial. See MD.