Follow up with your doctor because you don't have to be having anal sex to get warts in that area but it sounds more like a hemorrhoid. You can google hemorrhoids to find out more and how to get rid of them.
grace
In that case, it most likey is not an STD. However, I am not an expert! If you're concerned, just go see the doctor and see what he says. It's nothing ot be concerned about.
Have you ever had receptive anal sex? If not, then it's most likely NOT an STD