flesh on pad from withdrawal bleeding

I was on birth control for 3 weeks and now I'm on that one off week and as expected I got withdraw blood.
But when I took my underwear and pad of to shower, I would dispose the pad and put on a new one after showering usually, today I saw a big chuck like a sac of flesh with veins on it. It looks like a small tongue.
I don't know what it is and it's about 4cm long .
I don't know if it's normal.
This is my first withdraw bleeding
I'm also a virgin so before some of you say it's a baby or something, it's not.
I think it might be a big chunk of uterus wall.
I've had regular health periods each month since I was 13 and I'm 20.now but I've never seen something like this before.
?????

Deciduous cast I think it's called x

Deciduous cast I think it's called x

Deciduous cast I think it's called x

Thanks yh it wasn't the usual red blot clot chucks it was instead a pinkish vainy little bit of flesh. Thanks sooo much