That's very interesting -- I noticed the exact opposite effect. Melatonin helps me fall asleep faster, but sleep quality doesn't appear to be much better. I did notice an improvement in sleep quality with ZMA (zinc+magnesium+vitamin B6), and the melatonin+ZMA combo works wonders for sleep.

I've not noticed a difference with generic Kroger brand and other brands of Vitamin D3. Seems to be about the same effect. 5,000IU and 10,000IU aren't noticeably different in my experience, but either are a marked improvement over no supplementation.