Small, painless bump on penis shaft, just below the head.

First off, I would like to make it clear that I am a 16 year old virgin, and I have never had any sexual relations with anyone.

A long time ago (probably a year now, I've lost track) I discovered a small, semicircular, pimple-like bump just under the head of my penis. It's just that one bump, nothing else; about 2-3mm in diameter. When I squeeze it, it doesn't pop, and it's painless when I touch it. It's somewhat translucent, so that I can see a small speck of black in the center of it, about the size of a grain of sand. It doesn't cause pain and I haven't had any trouble with it, but it is bothering me. And I just want to know what it is, and what I should do with it.