Puberty is that stage in one's life, where the hormonal changes shifts towards the phase of being an adult. It starts in the age of between 8-13 for girls and 9-15 for boys. It is at this stage where your body releases special hormones to make you recognized as a full fledged girl or a boy. This is basically a natural phenenomena taking place internally which somehow excretes the hormonal glands making you look more matured and like a lady. Speaking of the blood leakage let me tell you, that it takes place after your breasts begins to develop which is also a sign of the first physical change in puberty. The blood leakage is more because of your age first of all and secondly due to the matured working of the reproductive system. However, this leakage eventually goes shrinking as you keep ageing.