I'm a 19 year old male and i'm tired all if the time and i sleep long periods of the day. what causes this and how can i prevent it?

Depression: The most common problem with this presentation in a young person is depression. Perhaps meeting with your family doctor is a good place to start to make sure it is nothing medical.

Depression: Depression may be the cause of your poor sleep problem. See a psychotherapist or psychiatrist for help.

Have it evaluated: There are many causes for chronic fatigue. See a doctor and have the issue evaluated to try to determine the cause.