You can take some herbal sleeping pills. Just take a smaller dose than recommended on the packet and they should calm you down somewhat. Take a test dose at the weekend though so you know how it will effect you before you go into an exam after taking them. You don't want to fall asleep in your exam!
When I had problems sleeping and took them I found I had to take more the recommended dose to get anything from them anyway. But then perhaps I have a high tolerance to them.