Confused? Passed tissue

I’m on birth control I’m on the week my period comes and yesterday I had some cramps then didn’t think anything of it cause I had to poop (tmi) I go to use the bathroom and I passed a very large piece of tissue. The thing is it wasn’t a blood clot it literally looked like skin.. I’m wondering what this could have been? I wish I would have saved it but I was working so I would just like some opinion.. I bled for one day now I’m bleeding when I wipe but nothing on my pad at all very weird