If your sure it isnt heart related then it sounds to me like it could be down to your lymph node in your armpit. Have a poke around, under and alla round your armpit and slightly around your neck and see if this is sore or tender. If it is, Im betting its a swollen lymph node.
I have these myself and have had a similar pain to what you described but mines because I have mono which is a little devil to your lymph nodes.
Your lymph nodes are also in your neck, below your ears, groin and armpits. If you ever have a sore throat or are very tired then I would have a Mono test done just to be sure.
Take painkillers if it happens again hun or have your hubby give you a shoulder massage. Works wonders!