Pain! :(

Hi,
Just wondering if anyone can help!
For the last few weeks I've had a sharp stabbing pain in my groin, like an inch below my hip bone!
It's always on the left side, it only ever hurts in the evening and a few hours after sex.
I've seen my GP and he said leave it for a while and see if it goes.
I want to know what it is! Has anyone had this before?