have u tried propping ur legs up? lie ur back and head flat and put pillows or folded blankets under ur knees to lift ur legs over the level of ur heart. sometimes mine ache so bad i put them straight up the wall. the arm of the couch works pretty good too.
good luck
If you sleep on your side, try putting a pillow in between your legs - this helps to keep the spine in better alignment.
If you are a back sleeper, you can try putting a couple of pillows under your knees to help keep the pressure off your lower back and hips. They also sell wedge type things made for this purpose also that tend to work better - mainly because they don't slide around like the pillows could.
The worst position for back pain is stomach sleeping - it's not only hard on the lower back, but also on the neck. If you typically sleep on your stomach, I would suggest trying to change to either side sleeping or back sleeping (I know it's not easy to switch when you're used to sleeping a particular way)
I hope these ideas help!