Hey DS, plenty of us have had a setback now and then. One thing to do, as I was advised on one of my setback / freakouts by my surgeon is to step back from activity for a bit and let the strain heal.
One of the possibilities is that your groin muscle is strained through normal activities and just needs to be babied a bit. If it persists, you do as you've done and let a pro take a look at it. If you're still in doubt, get a second opinion from one of the doctors listed here, but I would think that it is most likely a muscular thing.
I had one issue about a year along, where I got a sharp pain in my groin intermittently as I strode forward. It lasted about three weeks, then just went away. No idea why, but my doctor basically said to wait it out and that worked.
Hope it feels better soon.