Cat's anus has puss - any ideas?

[Bella and Cody]

Today I noticed my cat Bella was licking her anus. I've never seen her do this with such intensity before. I picked her up and turned her over and when I pulled her tail back to look at her anus a squirt of what looked like puss came out. She is active and alert. I grabbed a tissue and dabbed at the puss. It is yellow and is very watery. Any ideas or suggestions? I am calling the vet clinic to make appointments for both my cats but it my be a week or so before they get in since its a military facility. Does anyone think this is an emergency situation that can't wait? Thanks for your help! Aloha!