Sleeping at 20 weeks

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I've found that I'm really uncomfortable sleeping on my sides as if I'm suffocating. I then turn to my back and I'm totally comfortable and fine. I asked my doctor at the anatomy scan why I can't sleep on my back. She told me that is old news and the evidence behind it changed 2 years ago so it should be fine to sleep on my back as long as I feel ok. Anyone else sleeping on their backs?