Is it bad sleeping on my back at 32 weeks?

Yes. You should only be sleeping on your sides at this point. The baby's weight puts pressure on the vena cava which can cause a drop in blood pressure for you, and for the baby. You can sleep with a wedge under your right side to shift the weight, or on either side. No matter which you go with, you probably won't be sleeping comfortably for the rest of your pregnancy!