It isn’t normal to experience die-off symptoms for a year if you’re on the right diet and treatment.
Normally when the die-off symptoms decrease drastically but then grow worse again, especially if they do this several times, this is usually caused by the Candida adapting to the diet and/or they’re given enough time to adapt to a specific antifungal. Or … it’s because you’re feeding and killing the Candida at the same time for long periods of time. Feeding/killing can turn into a never-ending cycle that … well that never ends. So are you killing the critters only to allow them to repopulate the intestines again with foods on which they can survive?