I asked my nurse at 2 weeks post op when I could stop sleeping on my back and she said to return to my normal sleeping position whenever it feels comfortable to do so. It turns out it really wasn’t comfortable for me at all to sleep on my side until about 4 weeks post op. All surgeons and nurses tend to give different guidelines though so it might be worth asking your own nurse to see what they say. Personally though I think you’d probably be ok at 3 weeks, just make sure you’re not lying with loads of pressure/weight on your implants xx