Bad acid reflux but nothing is showing up in tests? What couldbit be?

I'm 14, and forever I've had bad stomach aches and nausea. Mostly it's just my stomach and that, but my chest does hurt every once in awile, so I do get heartburn once in awile. Recently the feeling has been getting kinda worse, and it almost feels like when I stand up and walk and stuff my stomach is pushing out and it feels like my chest hurts a little to. I never do throw up when I get the nausea, but its still annoying! I do feel a lot worse the week beforehand after my period. I just had an upper endoscopy done and they said everything looked perfectly fine, no bile build up or anything! I'm going to get tested for food allergies soon, and I think I'm going to the gyno because they want to see if it's hormone related because my period is like off because it's every 48 days. Is there anything Else you can think of it could be?