Question

why vagina produce blood and why cervix is large than hymen

Answer 1

In case of the egg cell is not fertilised, the thick uterus lining breaks down leading to bleeding. This is called menstruation or period
The hymenis thin and distensible, unlike other types of vaginal obstructions with thick obstructions [e.g. transverse vaginal septum (TVS), vaginal agenesis or cervical atresia (CA)]. Vulvar distension thus may arise in imperforate hymen, uniquely suggesting the cause of hydrometrocolpos.