what does it mean??

I have been seeing this pretty dark spotting ( like very black) in my underwear for the past 2days and also having this bitter taste in my mouth for about 3 weeks now. At first I tot it was the Spartans( my period) and it's due in the next 3days but there is nothing. No flow, usually after two days of spotting( light red) I face the Spartans. Maybe I'm just freaking out .