I think many/most of us have sleep troubles of varying extents...our circadian rhythms related to the pituitary gland...parent of the endocrine system...
The pineal gland is the one of maintaining circadian rhythms...and was once named the "third eye".
You may want to search on-line: pineal gland anatomy and physiology
and.... melatonin anatomy and physiology...
The image group pops up and, easy to view a page (site/article) or just of the image for the anatomy.
One site called "Rebecca's..." has a distinct image of the endocrine related glands. Her image displays the male/female bodies displaying the glands/other: pineal, hypothalamus, pituitary, thyroid, parathyroids, thymus, adrenals, pancreas, ovary and testes....
My involvement w/pineal came w/my pursuit in learning the limbic system...learning the hypothalamus connects to/controls our pituitary gland. Thanks to John in the UK who told us about the hypothalamus and its connection to the pituitary and our body temperature issues.
I hope the anatomy/physiology of the pineal and melatonin will help raise our questions to the various doctors...and, share back results with one another here.