It’s actually a general (and not necessarily genital) thing.
When my dentist performs my half-yearly dental check, she thoroughly searches for cavities, dental plaque and gum infections, and her very thoroughness might occasionally make me say “OWW” or “AWW” (mostly under my breath).
If medical professionals perform medical exams too softly, they might not find what they could be searching for (and they have to have a feel of the medical site after all). To add insult to injury, it’s generically the sensitive areas that are affected or infected by disease in the end —
And in those cases the occasional “OWW” or “AWW” usually mark the spot.