Period,Stress or Implant

My periods are usually around the 20th...i forgot to log last months. Waiting for this months. It say im ovulating now. But today at work (fed ex) idk if its stress or period or implantation. I went to pee And dark blood I seen on my tissue. Im not sure. Never happend before. I have been stressed and recovering from a head injury Latley But something is telling me pregnancy even before today. Can u guys fill me in and help?!?!