Could I be pregnant ?

Saturday the 14th I had brown blood when I went to the bathroom later that day it has cleared up ... Could it be implantation bleeding ? Wednesday I woke up took a pregnancy test because that is the day Aunt Flo is due it came back - & later that day Aunt Flo came but she was Heavier than she has ever been but she's gotten lighter as the week went by ..even if I'm not pregnant does anyone have a clue about the brown blood ?