Meant to add that he looks like a Yellow-Bellied Sapsucker, but much smaller. Maybe mine is just young?

I think you are right with the yellow-bellied sapsucker guess, and because of its size, it must be a young one.
The fluffiness does make them look different! But the red on the crown and throat is there, the messy black and white on the back, and the white stripe down the side is there I think, although hard to see because of the fluff.
I am only a very new backyard birder and used the Cornell Lab site to check this out. I hope I've been helpful!

It's an adult male yellow-bellied sapsucker. Size has nothing to do with age - except for water birds that leave their nests right after birth, pretty much any type of juvenile bird that has fledged is going to be the same size as an adult. Maybe this one is on the small side, or is missing a tail feather, or just the angle he's at makes him look smaller.

Thanks for the info, both of you. He was at the feeders all day, and looked to be the same size as a Downy Woodpecker. Maybe he's the runt of the litter. :-)

I'm happy to see him--my first YBS sighting in all the years I've been feeding birds here.