Your post could have very well been written by me. I have gone through (still am) so much confusion with heart-vs-GERD issues and I know how worried or uncertain you can be.
Since you have had heart tests done, the next step is to see a gastroenterologist.
You mentioned you take Nexium. Does your chest pain go away after taking it, or does it persist?
Get well soon.
"Don't just think positive, BE positive."