You need better shoes and probably a cushioned mat to stand on. The shoes are pricey, but worth it, and you can write them off on your taxes most of the time. My husband wears Dansko Professional Clogs to work and they have made all the difference in the world for him. Nurses wear these, too. They run about $120. The mats are inexpensive, check for "restaurant mats" online or places like Ollie's or Big Lots or Bed Bath and Beyond for those.
Unless you HAVE to, or it doesn't matter if you do or don't quit financially, if I were you, I would try those things before quitting. I can stand 12 hour days in the right shoes, too, and I have a bad knee that's healing right now ;)