Brown CM CD 9

So AF came and lasted 5 days, i have been off of AF for 4 days (im on CD 9). I’ve just started tracking my ovulation this cycle with wondfo opk’s and they are currently negative. Today when I went to use the washroom, I noticed there was dried blood in my underwear and when I wiped, it was pink. After that, the blood was gone. What could this be? My period has been done for 4 days and it’s Too early for ovulation..I couldn’t have gotten pregnant while on my period, could I?