HAPPY UPCOMING NEW YEAR!

So, I recently started having sex with a new partner. This person is only my second partner and I tested clean of STIs before sleeping with him. So anyway, today I was getting ready to enjoy a sweet orgasm to lull me to sleep when I noticed one smallish bump on my labia. It felt good to scratch, though it was not necessarily itchy and it is slightly painful when touched.

Now, I grew up with more than a healthy dose of Christian guilt, so my immediate first thought is "Fucking shit, you got yourself an STI, way to go!" But I also know that I sometimes overreact when it comes to stuff like this. Besides, most of my research says that STI's usually manifest as rashes or multiple small bumps. So my question is, am I overreacting? Or is this something to be concerned about?

FWIW: The bump is slightly red, shiny, is actually more shaped like a grain of rice, and is smaller than a pea, bigger than a lentil.

ETA: Thank you everyone for the advice! I think it may be a cyst or an ingrown hair and I'm going to try my hardest to leave it alone. It it gets worse, straight to the gyno I go!

ETA2: IT'S AN INGROWN HAIR! YAYY!