[Coda]

I've had a scare in the past thanks to costochondritis. (I didn't know that's what it's CALLED until, but I had a persistent sharp low-grade pain on the left side of my chest that lingered for several days and the description matches what my doctor said.) I don't think that's what you're dealing with based on the description -- that wouldn't cause a small localized pain for a few seconds every few hours; it would be a more continuous pain.