I can't sleep with my boyfriend. (literally!) Help!

I literally can't sleep with my bf. We can be all cuddled up and cozy, and I will be so sleepy and tired, but I can never fall asleep. Even when he's stuck to his side of the bed, there's just this little bit of awareness that just won't go away. The last two times he's stayed over, I've ended up sneaking off to the sofa after spending several hours just lying awake - and feeling cozy & content with that btw, but a girl needs her sleep.