He may not feel the need to use the hide becaue he is already in the tub, and feels secure, plus they almost never eat while on antibiotics, you should post a pic of the snake so we can see how thin he looks...
Plus if he is moving around a bunch it sounds like he is not ready to up and die.
I would not euthanize until the snake looks like he will not make it. From what it sounds like he is not anywhere near that point, let the vet finish the course of treatment, and you should bump up the warm side temps to 93F or so. make it slightly warmer to promote healing