I have exactly the same problem. My mum says its anxiety.

5 years ago I used to have a cigarette before going to sleep, and it worked for a while. Then I got hooked. Trust me, my pattern is really messed up, sometimes I'm up all night, or all day, sometimes both, completely unable to get to sleep.

For a while having a spliff worked well, but that guy's right. Once I started smoking it during the day as well it wouldn't help me sleep at night. At all.