Sleep positions

I have always been a side sleeper. Now that I'm pregnant I flip flop all night. I use a pillow to wrap a leg around and prop the belly on. I also put a pillow against my back for when I flip or flop. However, every time I wake up in the night I'm flat on my back and have no idea how long I've been there. I've read this position is dangerous for baby because it blocks major blood vessels and can decrease oxygen to babe. Anyone else having trouble? Any suggestions on how to stay off my back?