B737-800 FLT CREW HAS A TRACK HDG DEVS ENRTE MIA.

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ON TRAVELING BTWN DIW AND THE POINT JORAY; ATC INQUIRED WHERE WE WERE GOING AND THAT HE WAS NOT USED TO US BEING ON THAT PARTICULAR RTE. I LOOKED AT THE FMC AND WE WERE PROCEEDING DIRECT JORAY. HE THEN SAID WE SHOULD PROCEED DIRECT BGDOG AND THEN TO JORAY. NOTHING ELSE WAS SAID AFTER THIS. WE WERE DEVIATING FOR WX AFTERWARD; AND THEN PROCEEDED UNEVENTFULLY TO MIA. WE HAD BEEN GIVEN DIRECTS PRIOR TO THIS AND POSSIBLY WE LOST THE AR22 PORTION OF THE FLT PLAN. WE ALSO WERE PREPARING FOR THE UPCOMING WX ENRTE TO MIA AND WHAT OUR PLAN OF ATTACK WOULD BE IN NAVING THROUGH IT. WE WERE ALSO REVIEWING UPDATES TO THE MIA ATIS WHEN THEY WOULD COME OUT DUE TO TSTM ACTIVITY AT THE ARPT. ANOTHER FACTOR IS THAT WE WERE BOTH FATIGUED. I WAS DUE TO THE FACT IT WAS MY 7TH DAY ON DUTY DUE TO ADDING A DAY TO MY PREVIOUS SEQUENCE. AS TO EXACTLY WHY WE WERE FLYING DIRECT JORAY; I DO NOT KNOW. THE CTLR ALSO WASN'T SURE AND MADE NO DEAL ABOUT IT OTHER THAN DIRECTING US TO BGDOG. I CERTAINLY BELIEVE THAT 7 DAYS ON DUTY IS SETTING ONE UP FOR MAKING ERRORS AND MISSING INFO. EVEN THOUGH THERE WAS A FULL 26 HRS BTWN MY 2 SEQUENCES MAKING ME 'LEGAL' FOR THEM; I BELIEVE THAT OPERATIONALLY YOU ARE WAY TOO TIRED AT THE END OF THE 7TH DAY TO BE ON YOUR 'A' GAME.