my 2 yr old siamese-mix male, leo, seems to be having some issues of late. one, he is overweight. i have tried changing food and giving less, but it does not affect him. plus, i have a perfectly normal sized female calico who i do not want to underfeed. yet in the last day he does not seem to be eating. second, i beleve he is having digestive issues, i just noticed his anus is very dirty, (i thought it was blood @ first and had a slight freakout moment) but he is straining w/nothing coming out. third, he was a shelter cat, and we litter trained him, but he refuses to use the litterbox to defecate. he will urinate but not defecate. i dont think it has anything to w/my other cat, because they get along very well. both my cats are fixed and get regular visits to the vet (i am thinking of taking leo to the vet on friday if he does not get better). leo is acting slightly strange (a bit more whiny than usual) but otherwise is acting pretty normal. any help w/my baby boy would br appreciated. thanks!