How long does it last on average ? I have heard it could last four days! Seems a bit much for just a small membrane .

Also how much is it normal to bleed?

It really depends on the person. I myself, only had one little spot of blood, and that was the end of it. If it bleeds for more than a week, see a doctor because something could have been damaged :)

I had a lot of blood the first time but it didn't continue on it stopped after an hour. The second and third time was a lot less and after that I was okay.