Something somewhat similar happened to me a few weeks ago, except the pain was a little bit higher up - around the area where I have menstrual cramps. It was very sharp pain that lasted for several hours after sex (although the actual intercourse didn't hurt!), and it happened twice in one week. I was very worried and went to get an ultrasound, which came out normal. We just had sex again for the first time since those incidents and I was fine - no pain at all! I chalked it up to just random stress or strange positioning.

Hope you feel better soon.