What is this thing on my toe?

I'm a dancer, and a few months ago I noticed what I thought was a callus on my "ring" toe. It's right where my pinky toenail would rub against my other toe. I thought it was just from tight dance shoes and didn't really pay that much attention to it. Only recently have I tried to sand it off with a foot sander. The last time I did, I got it down to where it was almost gone, but it started bleeding. It's been about two weeks, and I've noticed that it's starting to grow back. And I haven't danced since the middle of April and worn mostly flip-flops since it got warm. So is it a callu or something else?