Yes, that sounds very much like a stressed Ivan. Hang in there sweety , Ambercat will slow down soon and as soon as spring arrives he will be outside very often.
No thyroid issue. Bloodwork is great, no signs of anything "sinister" on x-ray, ultrasound pretty much confirms IBD. He had it pretty bad when Daisy was alive, as she literally hated him, and he was always on edge. Then when she passed, it went away completely. I think it's stress related and the kitten has him a little on edge. Hopefully when Ambercat slows down in a few months Ivan won't be so stressed.
Ivan back from the vet. Kidney infection is gone, but he's still dropping lots of weight. Had an ultrasound done, and it looks like he has IBD, so he got a shot that should clear it up for a few months if that is the problem.