try laying in bed with a pillow under your back or on your side with one between your legs fluffier the better. or lay on a soft surface floor get a chair & put your legs in the chair that helps to. good luck. u could b having back labor pain if it is that bad.
The baby may be laying funny and putting pressure on your spine. Try laying on your left side with a pillow between your legs....see if the baby changes position. You could also sit on all fours (knees and hands) to see if it moves. While there round your back like a cat, then lower the belly to the floor...may help loosen it up and feel better for ya:)