Does anybody know why I cant sleep at night-even when I feel extremely tired?

Emily, You have some kind of sleep disorder and the only way to tell by having a sleep study done in a sleep lab. I would try something that helps me it's called Melatonin and it is purely natural sleep aid, it is found in most department that have natural remedies, the drug i'm talking about has serotonin which is one of the natural chemicals our own body makes that aids in sleep. I hope this helps u it does a good job with me. Good Luck