What could be causing this chest pain?

It could be heartburn. Does it burn? Or is it like ice? That would probably be a heartburn.

When I don't eat enough and am moving around (Even if it's not a lot) I can get heartburns.

I am glad your heart tests are good, but have you had a tilt table test done? Which tests the response of your blood pressure while on the tilt table. Also did the tests include a Holter monitor, which monitors the cardiac activity over a 24 hour period. When does the pain occur, after you have been sitting or lying down, or standing for any length of time? and does your doctor know this. Has your doctor made any suggestions as to how to increase your blood pressure, e.g increase fluid intake, avoid coffee and alcohol. Ask your doctor if the pain your experiencing is associated with the low blood pressure. You may not be aware low blood pressure has been identified as one of many symptoms of Fibromyalgia, (but not all Fibromyalgia sufferers have low blood pressure) and with low blood pressure it may cause an irregular heart beat to be felt. I understand a little how you feel, as I have CFS and Fibromyalgia, and for me it causes low blood pressure from time to time and irregular heart beat, which can cause pain but I also have a heart murmur. I hope your doctor can help sort things out, and that you can feel a little better soon.

you could have anxiety. That's what I was told anyway.