Just finished my placebo week 2 days ago and now bleeding again!

I don't think this has ever happened to me. My placebo week ended on Saturday and I started taking my regular pills again on Sunday. My period always tapers off by about Friday and there's only a bit of rusty colored blood on that day. By Saturday usually nothing. That's how it was this time. I had absolutely no blood on Sunday when I started on my regular pills. I woke up this morning (Monday) and I had left a blood stain on the sheets and when I wiped I had a good amount of red blood.

Why would I be getting this again, and for it to be so red, when it just ended? Also, I did take my pill at the right time so it's not like I forgot or was late.