Implantation, period, possible miscarriage???

Need help with whats going on. Im currently 13 days late. On day 7 of being late took a test and it came out negative. I have irregular periods but i've gotten really good at predicting when it will come. 2 days ago I had some brown discharge that turned into bleeding. That lasted about a day in a half. I've had no pms systems that I normal experience. I asked a friend what she thought and she said it's only happenedto her once before and it was a miscarriage. The bleeding I experienced started brown then it was red. Thought I saw very small clotting in it but could be wrong. Does anyone have an idea it might be?