The blood from your period comes from the tissue that lines your uterus. When you ovulate your body flushes the whole system out by breaking down the lining of the uterus. The reason you get cramps and such is because the muscles in your abdomen are contracting and squeezing to help the process along. It takes a few days normally to finish a cycle, but usually it shouldn't last more than a week to a week and a half.
