I actually think it is super interesting that you mentioned working out in the evenings as a way to put yourself to sleep. I actually find that I struggle to sleep after I work out because getting my heart rate up actually wakes me more than it does anything else. I work out really early in the morning, generally between 5-7am so that I get it finished before work.
By making this part of my daily schedule I am actually getting exercise and keeping my energy level up. The only times I have a hard time sleeping now are when my mind is too active, which is generally a sign that I was not physically active enough throughout the day.
I too have tried melatonin, and it seems to work for me, almost too well. I overslept for the gym and woken up groggy on a few occasions.
QUESTION: do you sleep better when it is cold or when it is hot? Why do you think that is?