This is so crazy - I had almost exactly the same relapse at 3.5 weeks. Allow me to quote from my diary, pulled from about 3 weeks and 6 days after surgery: "what?! Seriously, this is longer than I’d figured - it’s been three days and I’m still sore, I still can’t walk without the cane, and I still have to take Tylenol from 5:30 on to get thru the night!?! What the [copulation synonym] did I do to my leg!?!"
While I managed to avoid the same degree of pain you're enduring (and I'm crazy seriously glad you're looking for more puissant meds!!), it was an astonishing demoralizing relapse, completely out of proportion to the sins I'd committed against my recovery. It took more than a week to get out of ODIC jail, and I was miserable, angry, and drained. Just a big ol' man-baby.
Is this a natural part of the process or ODIC? Dunno - too few data points. But in the mean time, hang tight, don't lose hope that this too shall pass, and do everything you can to alleviate the pain! Pain sucks! And you ain't got time for that [excrement synonym]!