please help!!

Samantha
I take Apri combination birth control pill; I take it everyday at the same time and have been taking it for a couple months, I have never missed a pill and don't use medication that would interfere. I used to get my period on the Thursday, 2 days before my active pills are done, but the past 3 times I've gotten it on the Tuesday of my inactive pulls. On Thursday, 3 days ago, I felt something run out of me and it was blood, reddish brown, so I thought it was my period. But then it just stayed as if it was spotting. It was in my underwear, as light brown with dark stringy clots maybe? Not sure. But then it was dark brown. And then it went to red, and I have been inserting tampons in and its red with some brown. Now today I left it in all day, this morning it was red, and now it is dark brown with stringy clots I think. Before when I wiped it was on the tp but now nothing. What's going on? Is this implantation bleeding? Or just leading up to my period? This is the 4th day of "bleeding"