I believe what you're experiencing is implantation bleeding. Have you had any cramping?? R you breasts tender and/or sore? If so, you could possibly be pregnant as these are some symptoms of pregnancy. I would recommend doing a pg test the day that you are due.
I understand what you are going through, i am too going through that my last period ended almost two weeks ago and i have had the same problem as you, there will be one spot through out the day for me of blood and then sometimes there is none, but then i notice when i use the restroom there will be a dot in there, you may be spotting like said above^^ i have been worried lately too and have decided to take a pregnancy test today after work, i just wanted to let you know your not alone, i hope this helped, you should also see your gyno or doctor and ask questions !
is there any chance you could be pregnant, it could be implantation bleeding try doing a test when your next due on, if not could you be anemic one of my friends was for a while and that made her bleed irregular just a thaught hope this helps. tex