Late caffeine is an issue for me too...
If not that, it's usually some pain or muscle tightness...try taking an aspirin before bed (if you're not allergic). Many benefits to this routine.
The majority of your growth hormone release and recover is in the first 4 hours of good sleep, but more is always better when you're lifting.
Can you take naps without messing up your day or sleep schedule?
"You must have a very strong reason for doing an exercise. If you don't, scrap it and move on." -Jim Wendler