When I can't sleep I take a shot of Nyquil
Had a friend that used to do this...he got addicted to Nyquil!!
Pretty much anything used as a sleep aid for long periods of time will become "addictive", in the sense that you have trained yourself to not be able to sleep unless you have it. (Even if it does actually help.)
I would agree at looking at sleep cycles. The other thing I would think of, is that this happens to me when I'm extremely stressed at my work place. (Mind and body are preparing for the strenuous day ahead.) I would recommend some meditation before bed to try to clear this.
This is a simple form of samatha mediation. Simply get comfortable somewhere, preferably in a room as devoid as sensory input as possible. Close your eyes, and simply concentrate on something. (Common focuses are breathing or a mantra.) Think about nothing else. If another thought comes into your head, do whatever you need to do to acknowledge it, then immediately go back to focusing. You'll find that the thoughts that are most persistent are usually the things you're stressing about the most. By acknowledging them, you are allowing your mind to stop worrying about them and relax.