I'm bleeding internally after Tummy tuck due to blood thinners. Any suggestions?

I just recently had a tummy tuck, one that I have waited years for. However, after surgery things began going wrong very quickly. After my surgery (4 days) I was admitted to the hospital for internal bleeding, required three units of blood and put on a machine that did my breathing for me, as my body could not do it for itself. Now I am stuck with another surgery to remove the giant blood clot. What went wrong? Did I need blood thinners? Thank you.