I ve been having shorter periods for the last couple of months now.They have only lasted anywhere from 2 to 3 days. I m not worried about that, cause I ve has irregular periods before. My only concern now, is that about 3 days after I end I ve had some discharge that is very dark brown, almost black. It s somewhat thick. I ve also experienced some lower abdominal pain ,during this. Is this just old blood , or could it be leading to something else? Some PMH you may need to know, is that I was recently dx with Endometriosis . I also have cysts on my ovaries. Could one of these be the problem?