Hi
Usually before an exam I do the following to sleep longer (and getting to fall asleep faster):

Stretch out for minimum 5 minutes.
Use a shampoo with herbs in it to stay asleep longer.
Use 10mg of Kestine (also called Evastin, Ebaste and Aleva)

1mg time released melatonin from Now foods.
About a half milligram of sublingual melatonin.

Foods that I eat:
Tomatoes.
Avocado
Salmon Fish
Some salad
And I also drink some milk and water.

I also avoid sugar and caffeine the whole day.

In addition to all this I try to getting at least 1 hour of exercise.

However, before my last exam I woke up after only 4 hours, what could be the reason for this? It is easy to fall asleep, but I really need to sleep for a longer time.
Thanks in advance