Melatonin is suggested by some to assist in the induction of sleep.
Here is a link.
http://www.ahrq.gov/clinic/epcsums/melatsum.htm
Sleep is a complex whole body thing so stimulants late in the day eg caffine, or high levels in the day may have an impact.
Improving diets balancing omega threes and sixes, looking at body acidity, salt intake etc. exercise may all help.
http://www.ncbi.nlm.nih.gov/entrez/q...=pubmed_docsum Nature is very complex for example I have read some salad vegetables have substances in that induce drowsiness so a wide variety of food should help provide the body the things it need to do the things it does.....
Melatonin is "controversial". There is some evidence it is an antioxidant and may reduce BC risks but again that is not well trialled. So please discuss with your advisor.
You will find lots on google on the subject of melatonin.
RB