Hello,
I am not able to diagnose online. But I do think that it would be helpful to find a feline specialist. I would also talk about adding sq fluids to be done daily at home and an appetite stimulant while you try to figure out what is going on. In some cases I also recommend in clinic iv fluids to help diurese the kidneys.
I hope this helps.
Very best of luck.
It looks like it might be a tapeworm? You can bring it to your vets office and they can help identify it. Also.
There is a lot of information about them online. I tell my clients to treat for fleas.