Hi hun, just wanted to put your mind at ease and say that if you do roll onto your back you'll end up waking up or rolling over (or waking up to roll over PMSL if you're in the last few weeks! lol).

I slept on my stomach until 14ish weeks, and then on my back until I really really couldn't lie on my back. If its not making you feel ill I wouldn't worry about it, its really quite early and the pressure won't be too great anyway. Oh, and the placenta being anterior won't squish the baby either (well, not as far as I know?).