My best guess would be giardia, mucous in the poop is a symptom, diarrhea, anorexia another. Here's a link. It's harder to diagnose than the other parasites and doesn't show up in a normal fecal float, but there is a stain test that is accurate, but some vets have to send this out to a special lab. The treatment prescribed is metronidazole (flagyl). This probably needs to be ruled out so it doesn't progress to bloody diarrhea. Get a fresh stool sample into a vet, many will test without an appointment for about $10.00. I would continue to feed the boiled skinless chicken and cooked white rice.
http://www.thepetcenter.com/exa/gia.html
Just noticed you posted yesterday. Sorry I just saw it.