What Causes Dark Red Bruise On Foreskin After Intercourse?

Alright so I was tested for STD s a week ago, and I was perfectly clean! I recently had sex yesterday with someone who was also clean. I woke up this morning with a little dark red bruise/ mole looking this near the base of my penis, on the foreskin. It does not look like anything an STD would cause, so I m worried it s cancer....