Dark brown blood first two days of period, then bright red with very large clots. what is going on? this is every month.

This can be common: It is not uncommon to have dark brown blood at the beginning of a period b/c this is usually old blood/tissue. Once the period gets going and the uterine lining is shed, the blood will look brighter and have larger clots. If this is a change in your period, then speak with your doctor as to the cause of this change. Sometimes periods are too heavy and cause anemia due to the excess blood loss.