By definition, the period is a cycle of being fertile and being infertile. Think of it as closing the shop for cleaning. On your first clear day, the uterus prepares for having a baby, the womb is clean and there is new "wallpaper" up that is the surface that the egg will attach to. The egg is being prepared in the overy, and will be delivered down the fallopian tube around day 12. If you have sex before then the semen will most likely fail outside the uterus, but it might survive so don't trust the "timing" method. When the uterus is ready to do business, it opens the doors by making the fluid that blocks the door to the uterus (the cervix) thinner so the semen can get in. If it does, and it finds the egg and fertilizers it, you will stop menstruating for 40 weeks. Then Bub arrives.
Otherwise, the cervical fluid thickens up, and the egg and the lining of the uterus gets old and the uterus needs another clean out. The female body does this by bleeding. First the fluid blocking the uterus gets thinner again, and the old lining begins to fall away; that's the nasty part of the cycle when stains and odd smells occur. Then the blood follows as the uterus is cleaned out. Blood clots can form in the uterus or the vagina, but typically they fall away. A woman might bleed for three of four days and lose an eggcup of blood in that time.
Women should see their Doctor if the pains are bad or last more than a few days, the bleeding is very dirty, pale, coloured other than normal, goes on longer than normal, or clots a lot.
I hope that helps but if not talk it over with a GP, compare notes with other girls, or mother, aunties etc.
Dr.Goodlove(non-medical)
Chat with our AI personalities