Off work..finally! But I have a medical concern regarding my period, so..my periods are usually the…

Off work..finally! But I have a medical concern regarding my period, so..my periods are usually the same I have a 4 day cycle it's light the first day and heavy the second then the third day is light then the last is spotting...well for the past 2 months at the END of each cycle like the last 2 days. I have black blood?? I know usually it's brown/red at the end but for some reason it's darker??? Any one else have this?