Please assist me -  I have no idea what'  s the cause of this?

I am in a stable sexual active relationship.

I last had my cycle in the end of September... I am on Yasmin tablets. Recently I have gone through a very stressful time -  very stressful! Monday I was in a car accident. I was suppose to start my cycle about 1 and ½  weeks ago, Wednesday all of a sudden when I got up off my chair I felt this sense of relief in my lower tummy area, with also pain at the same time. If I can compare it, it feels the same way if you wee wee and you have been keeping it in sense of relief. When I looked down there was blood running down my legs. I had to go change pants and everything. When I went to the Toilet to clean up I saw solid pieces -  . Small. I'  m not sure of these pieces were pieces of growth, meat or what it was. There were also some white in between. It also seemed like very dark blood. I have been bleeding very heavy since this.

I have never been to a gynae -  I have made an appointment but can only be seen Monday.

Please assist -  this has never happened to me -  my monthly flows is normally not even near this heavy. It just keep on flowwing...