The white discharge that you are experiencing is a normal physiological discharge known as physiological leucorrhea. When mixed with normal menstrual blood cause pink vaginal bleed.
It is completely harmless and part of every woman's life. It has no relation to sexual intercourse and is not a form of infection. It occurs due to an imbalance in the normally occurring bacteria in the vagina. This is due to excessive estrogen that is present in the adolescents.
I would recommend the following-
1) Maintain a good hygiene around your privates. Do not wear tight clothes as it may increase the chances of infections.
2) Maintain a healthy diet that is not high on chocolates, greasy food, white flour and tea.
3) Proper sleep and exercise are important for the regularization of estrogen and progesterone.
4) If the discharge becomes excessive or if it cause any form of social embarrassment consult a gynecologist for the use of oral contraceptive pills. They help in regularization of hormones and the best treatment for physiological leucorrhea.