Just to disclaim that I'm not a nurse or medically trained, but honestly, if you feel more comfortable, and haven't put on stacks of weight, and you don't experience any of those side effects, then I think being comfortable is really important. You need your sleep etc. I can't imagine one or two nights would make that much difference, because in all the warning of how you shouldn't sleep on your back, they always say "if you wake up on your back just roll over - you haven't done any harm to your little one" so I'm guessing a few hours on your back isn't that big a deal?? But just give your obst a ring, or your care provider - you've tried all the pillow positions I suppose??