Hi Caspian,
You were so helpful to me about year ago with my American bullfroglet. My frog is now about a year as a frog (she'd been a tadpole that we raised).Anyways,she is acting very lethargic too and barely eating. I share your concerns but have felt it must be due to Winter, since she appears to be otherwise healthy Does your frog have a slimy viscous film on his lower body? Mine does and I'm not sure what that is about.