It sounds to me as if you changed up his world just as he was getting used to it. Exactly how many months is a "few" that you've had him, because you said you
changed his enclosure completely about 3 months ago ("12 weeks")? So while I know you meant well, it seems to have set him back? Either that or he's noticed
the shorter days & maybe lower ambient temperatures of fall & that's why? I hope someone has more ideas for you than I do... How old is he? Did the previous
owner/breeder ever brumate him for breeding?