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Pain at your collar bone, like a muscle cramp? Let me tell you a story, and you decide if it applies to you. I'm going to suggest the possibility of a particular muscle being tight, on the left, one that attaches to your collarbone and sternum. When you read about it, you'll see why I say it. The muscle isn't really suited for direct massage, because if the Vagus Nerve is pressed too hard, it will cause the heart to be slowed, or stopped for a bit. There's some anxiety on what the problem might be, I hope I can help.

The muscle is the Sternocleidomastoid. First site shows its location, also some symptom sites. Notice that the sites are all over the area, including multiple locations at the head and the neck. Especially that one at the collar bone. If you're not having all those other symptoms, count yourself as fortunate.

How to find out if this could apply to you? That's an easy one. Stretch it. With a special stretch, and the next two sites tell you how to do it. And if there is any difficulty in either direction, work to it slowly and gently, because you'll know you're getting closer to getting it resolved, and may have found what's causing the problems. And be sure to alternate directions for the stretches, since doing it to the left is stretching the one on the right, and I expect that there is need for stretching both of them to be sure to deal with, and to prevent the other issues you haven't gotten, or didn't attribute to a tight neck muscle. Be sure to include the upturned head portion of the stretches.