BLEEDING AFTER PERIOD. WHAT DOES THIS MEAN?

I HAD MY LAST AF ON MAY 25TH...IT DIDN'T LAST VERY LONG...ABOUT 3-4 DAYS...AND THEN TODAY AT WORK AFTER USING THE RESTROOM, I WAS SHOCKED TO SEE THAT I HAD FRESH BLOOD STAINS ON MY UNDERWEAR.  I DIDN'T SEE IT THIS AM WHEN I WOKE UP.  I HAD BEEN ON THE PILL THE LAST MONTH AND THEN STOPPED LIKE 2 WEEKS BEFORE MY PERIOD BECAUSE I MISSED SOME PILLS ALREADY.  WHEN I DID GET MY AF, I GOT BACK ON THE PILLS, BUT ONLY FOR ABOUT THE FIRST THREE DAYS...BECAUSE DH AND I HAVE DECIDED THAT WE WOULD TTC.  SO NOW, THAT I SAW THIS THIS MORNING, WHAT COULD IT MEAN?  IT COULDN'T BE IMPLANTATION BLEEDING COULD IT?  I'VE HEARD THAT IMPLANTATION BLEEDING IS BROWN...WHAT I SAW TODAY WAS RED.  I WON'T KNOW FOR SURE HOW LONG I WILL BE BLEEDING BUT IT SEEMS VERY LIGHT AT THE MOMENT.  CAN SOMEONE TELL ME WHAT THEY THINK IT MIGHT BE?