can which relieves with nitro is usualy dud to coronary artery
disease but as u said u have done stress
echo which came normal so there is less likly chance but there r some cases in which stress echo was normal but pt found out to have coronary artery disease so the best non invasive test for u to rule out coronary artety disease is CT/MRI
coronary angio which will give u best idea about ur coronary artery. hope i solved ur query.