Sneezing a lot

So my big guy who is 8 years old started sneezing a lot multiple times a day probably on 9-9-26 when it initially started . I would say today (Sunday) and yesterday he sneezed the most. I have 2 other kitty’s whom are fine but anywho. I noticed yesterday he scooted hit fanny on the floor and he smelled foul in that area. He has done that as well one or two times over a year ago. I have a vet appointment Tuesday. Any advice on how to comfort my baby. I’m watching him like a hawk to make sure he is at least using the bathroom.