That's how my issues started, a sore bump about the size of my pinky nail, just thought it was an irritation at first, then found it when wiping. It got to thumbnail size, then hot sitz baths let it burst nd drain. Unfortunately, it turned into a fistula, and I had to have a seton placed.
Show it to your surgeon. That's my best advice to you. They need to be aware of it.
If it gets worse, ask for a pelvic MRI, especially if it starts a "fill, drain, burst" fistula cycle.