Ahhh mama, back pain at this stage is SO common, you're carrying so much! But since it's bad enough to keep you awake, definitely check with your gynae or go to the clinic, okay? They need to rule out anything serious, especially at 33 weeks. A few of us mummies found that sleeping on our left side with a pillow between the knees helped a bit, and warm (not hot!) compresses also gave some relief. But please don't just push through lah, your doctor needs to know how bad it is. Take care of yourself!