Hej @Rebars papa, welcome to EBN I'm sorry you're having problems with Rebar What comes to mind for me is a possible obstruction... could he have eaten something he shouldn't have? A bone, a piece of a plastic toy, a sock? anything? I would take him to the vet to be safe.
Please keep us posted on how he's doing, hugs to the little guy, hope he's feeling better soon.