Could it be a freckle? A normal skin variation?
If it's smaller than a freckle, it's not likely to be HPV, which would be the only possibility for an STD.
It could also be something called angiokeratoma of Fordyce.
There are a lot of possibilities, but the only way you'll know is to get it checked. It's worrying you, so it's worth your time and money to get it looked at. Let us know what happens.