Is this implantation , spotting ? please help ?!?

MY FIANCE AND I HAVE BEEN TRYING TO PRODUCE A CHILD FOR A FEW MONTHS NOW.. WE HAVE UNPROTECTED SEX OFTEN , WELL EVERYTIME WE HAVE SEX. AND MY PERIOD IS LATE. ON MONDAY WE HAD SEX AND I STARTED BLEEDING, NATURALLY I THOUGHT IT WAS MY PERIOD.. HOWEVER AFTER A FEW HOURS IT WAS GONE AND THE FLOW WAS VERY LIGHT LEAVING A BROWN SUBSTANCE ON MY PANTIE LINER. WE TRIED HAVING SEX AGAIN TODAY & AGAIN I WAS BLEEDING, BUT IT STOPPED RIGHT AFTER... WHAT IS WRONG? COULD THIS BE A SIGN OF PREGNANCY ?