Menstruation comes five days later. Today, I masturbated and lost a lot of blood. What happened?

That's because when your period comes, it is likely to be 7 days before the previous menstrual period. Besides, if you stimulate it, it will advance your period. It's normal not to worry too much, but if there are adverse reactions afterwards, you must treat them in time. General gynecological diseases can't be delayed!