do you feel it coming on?! Or do you wake when its full blown agony?!
If you wake up when its just coming on, straighten your leg, and bend your toes towards you, it stretches the muscle the opposite way to the spasm in your leg and sometimes help relieve it. Never point your toes away from you though, as you will just help the muscle spasm and it will be even more painful.
Another one which is good, if you have laminate or tiling in your room or a close room, stand with your foot flat on it(i know it hurts and its hard when your hobbling around), I always find cold surfaces help. I used to put my foot up against the wall!!
Try massaging your calves for 5 mins before you go to bed, this helps relax the muscle

and also hot bath before bed or hot water bottle.
I know the pain hun, i HATE cramp!! But I used to suffer with it badly before I got pregnant, I was even prescribed drugs for it! But I found these few things helped. x