What a great idea! you remind us, there are many things that might help, which are not an interference to the wfast.
Reflexology might help. (but don't overdo it! This can stir up toxins.) Maybe even an enema?! (Though admittedly, I've never done one, on a wfast, or off.)
It might also come down to a bit of 'better luck next time', in the sense that if there is caffeine withdrawal contributing, it will be best to prepare--for the next fast.
It's a learning curve, for certain.