What Causes Bright Red Menstrual Flow?

hello my name is Dayna... i have a question about my period. well for the last 3-4 years i've had my period for 3 days and it has always came out dark red to black. i always thought it was normal. and well i just got my period again this month and it was bright red and lasted for only 2 days. i want to know if its normal..