Swollen gum in 4 month old kitten.

Just noticed one of my new Sphynx kittens has swollen right top back gums. They both have horrible breath (always have) but only one has swollen gum. I brushed their teeth last around a few days ago and her mouth was fine then. I'm really worried and wondered if anyone has any advice or knowledge while I wait for vets to open.

Hello!  Sometimes kittens that have had certain viruses get extremely sore gums, on a chronic basis, afterwards.  But this seems to be a single tooth in a single place, so I wonder where your cat is with their teething pattern?   Could this be a tooth erupting?  The two sides don't always develop simultaneously.   Always check with your vets if unsure.