You could be describing the last two weeks of my life. I hope by now you've had your problem diagnosed, but on the chance someone else comes along with the same issue, I am answering your question. I've had pain in my right collar bone, going through to my back, up my neck, and slightly down my right arm, along with horrible heartburn and indigestion. I was diagnosed with acid reflux and given nexium 40 mg once per day. I've taken it just once, and it does appear to be helping, though I've heard you need to take it several times before you will get the full effects. Of course, other things can cause these symptoms, and you should never risk your health and should always see a doctor.