I'm curious as to what dosage you're taking. Several sources I've seen suggest the dosage they recommend on the package is too high for many of the typical brands out there. Do you experience these symptoms when taking low-dose melatonin (<= 0.5 mg)?
I've tried both high and low dose, and many different brands. Effects are the same either way. I usually go with the high dose since I'll only be taking it for one night anyway.