Hey,
You may have pulled a muscle. That's what happened to me. Rub some Tiger balm on all the areas that pain you when it acts up again and if the Tiger balm or a heating pad and taking an aspirin makes it feel better then it is a pulled muscle.
Don't go spending a lot of money on hospital bills if you don't have to. I ended up spending $2,000. over a pulled muscle and your symptoms sound the same as mine did. Pain from the sternum around the rib cage all the way to the back at the tip of the scapula. It hurting while breathing in is another sign you pulled or strained a muscle in the rib area.
Where you doing exercise or lifted your arm in an unusual way you usually don't?
I'm not a doctor but from my experience, it's probably a pulled or strained muscle/s.