Is there a way to go back to the beginning of my Facebook page and efficiently delete everything I posted up until today??

Not in one go, but, if you have Chrome or Chromium, there's this: "Social Book Post Manager" Chrome Extension Lets You Wipe Your Facebook Profile

(It's not really your "profile" it manages, but your posted content.)

N.B.: It will take several passes, perhaps over several days, for it to do a complete job. I select my date range, let it run at full speed, then re-run it at lower and lower speed settings. Finally I go through my activity log manually and clean up the stuff it misses.