Can't Sleep

I'm getting really tired of not being able to sleep.

I can fall asleep easily, in fact, I fall asleep on the couch or chair well before bedtime sometimes. Other nights, I go up to bed, turn out the light and fall asleep immediately. I just wake up so darn early! 3 am. 4 am 5 am 6 am (which is fine for the days I work) I want to be able to sleep in.