I know exactly what you mean, I had and sometimes still do get exactly the same pain in the same place although mine doesn't go to shoulders or back. I was really worried about mine as like yrself mine used to make me cry and make me feel physically sick.
People said to me that it could have been trapped wind and after a visit to the local accident and emergency dept at my local hospital they confirmed it wasn't, and couldn't tell me what it was. I got myself some tablets called windeze and they cleared it up straight away, so maybe it was trapped wind after all (but who thought that wind could be so painful, definately not me). Like yrself I haven't got a clue what brings it on and thankfully haven't had it for a little while now, so maybe if yr's keeps reoccurring you could try different types of wind relief tablets until you find one that suits you.