Must help son poop

Ok on Sunday my son ate used kitty litter. He hasn't had a bowel movement on his own since before he ate it and both poison control and the doctor are concerned but would like us to try other methods to help him pass it since he doesn't have the vomiting and other things that go with a typical bowel obstruction yet. Since he's seemed uncomfortable and won't take the laxative we've given him a glycerin enema hoping he'll pass it but all he can manage is a little liquid poop and a lot of mucus. The only solid matter in this kids bowel movements is mucus.
Also he seems to be sick,no fever but all he does is sleep, he's not eating or drinking as much as usual and he sounds really bad. The doctor said not to worry about it unless he gets a high fever but this looks a lot like something the cat just got over and we know that the cat picked it up from fighting outside. Does this sound like maybe we should take him back in soon? What can I do to help this kid poop? FYI tried Miralax and prunes and he just won't eat them.He's really picky and he's pickier when he's sick.