I once had a hernia. It was discovered during my physical, so I had no idea how or when it happened. Someone, a UPS nurse I think, asked me how I suppose I had done it. "Lifting heavy boxes at UPS", I answered. Nothing else happened, I went on comp, had it fixed.
Just sayin', anyone who suggests this happened outside of UPS is gonna look like a fool. You lift heavy items every day for a living, of course that's where it happened.
Maybe they'll screw with people they think they can get away with it with, maybe I'm the type they know not to fool with, I don't know.
But I'd file that claim right away.
You already went to a doctor? So what, you had a pain you wanted checked out. Now you're filing because OF COURSE it happened at work.
Haven't gone to a doctor yet? I'd lean towards doing what
@IESucks said just to be safe.
Good luck, either way file tomorrow.