Sleeping on my back!

I've never been a back sleep but since becoming pregnant I can't help it.. I always wake up on my back and it's more comfortable.. even when I fall asleep I can feel my body twisting to get onto my back so I know I spend a lot of my sleep on there.. I've tried putting pillows to stop me but it's not working. I'm quite tiny for 29 weeks and it doesn't make me feel sick or dizzy will this be okay?