Ree, that is what it could be. I had one a few years back and it got to well over golfball size but by the time I got in to see my GP it had gone down enough that 1 he didn't need to lance and drain it at the hospital and 2 I didn't need antibiotics. It was extremely painful and I had no idea what it was because I'd never had one before so you can imagine how worrying it is!

Emc, yep they are on the inside, but when they get infected like that, they become quite large and you can certainly feel them in the area Ree described. A cyst isn't always painless either.