Light Pink Flow Turning Into Brown Discharge, Period Isnt Due. What Could This Be ?

Hi, i started having a light pink flow about two days ago. During the afternoon of the first day it turnedbinto a brown discharge. By the next day, the discharge became bright red and by last night it was dark brown and almost black. Its not a lot like a full period but its a lot more than spotting. Im not on the pill, my bf and i havent had unprotected sex during my fertile days. Im kind of freaking out. What could this be? Oh! Also, this started halpening during the tine when i should have ovulated. My period isnt due until the end if the month (26th of May). Please help!