Many doctors say to sleep on your left side b/c circulation is better. However I can never fall asleep on my left so i usually end up falling asleep on my right side. And it DOES get uncomfortable, my shoulders and legs start to cramp and hurt :/
I think on your left side is the best position for circulation to the baby.
Left side is best once you start getting bigger. You can sleep on ur tummy until your unable to from ur growing belly. I cant sleep just on my left side my legs get severe cramps so i rotate allllll night.
I've read the left side supported by a body pillow. I've always been a back sleeper & at 17w4d i still continue to sleep on my back just elevated. I know its known to be a no-no but my Dr said its safe as long as I'm elevated & comfortable. Hope that helps!