Hey there jerseycity,
I am not sure what your Dr. meant when he said your heart does not relax normally. The only thing that comes to mind would be cardiomyopathy. The heart muscle in people with restrictive cardiomyopathy becomes rigid and less elastic, meaning the heart can't properly expand and fill with blood between heartbeats.
I am glad you are seeing your Dr. tomorrow so please let us know what you find out. We are all here for you.