Heart flutters, chest discomfort, sharp head pain?

I've had a most of your symptoms and I notice that when someone put pressure on the left side of my back, right beside the shoulder blades, it went away. I talked to my meuse, and she told me that it was a stuck muscle that goes from my back all the way over my shoulder and down to make chest that gets stuck. I'm no doctor and not 100% sure it's the same thing, but it sounds like it. She gets it unstuck on a regular basis, and I feel better. You say it happens at your part-time job, does your job involve you lifting or using your back? I was a cashier at the time and I've seen other girls with the same thing. This is only from personal experience, so you should probably still ask a doctor. I hope this helps you not worry too much until then.