Yes, during your period, your body will release anticoagulants that keep the blood fluid and thinned. However, if your flow is extremely strong, the blood may pass before the anticoagulants can work. In this case, the blood may clot as it is passed.
Yes, blood clots during a period can be very normal in woman. It usually is just a sign of blood passing on too quickly. However, if you feel abnormal about it, make an appointment with your OBGYN to get a pap smear.