Melatonin has been referred to as a "dirty substance" and can potentially cause undesireable side effects. I heard recently from someone else who suffers from severe insomnia that UNISOM or it;s generic equivalent (I forget the actual drug name, I had it written down somewhere) works wonders when nothing else did. It's OTC, and you can get the generic at Walmart I believe.
I sympathize with anyone who cannot get quality sleep. Ive never had that problem and I cant imagine it's a good feeling.