Medicines lose potency over time, but they generally don't become toxic if stored properly, etc.
I've thought something was expired, but after looking closer it was a manufacture date and said to use within 24 months, so double check if possible. Worst case, you might have to retreat per...
The only thing I would add to what you are doing is an electrolyte and probiotic, maybe try moistened feed to encourage eating.
I am having similar issue with one of my girls and it started about the same time frame, she is doing better so far with some TLC.
Just curious, have you also been...