I have never been told to sleep on a particular side I find it most comfortable to sleep on the right side now having migrated from sleeping on my back which became increasingly more uncomfortable as I have been getting bigger.

I also find using my triangle pillow helps also by slipping it under my belly or by wrapping it around towards my back to ease the strain. If you don't have a triangle pillow then an extrea pillow should help in the same way

Nae x