In the early days of pregnancy it is fine to sleep on any side.. From 2nd trimester onwards sleep on left side and avoid sleep on back side.
Sleeping on left side position allows for maximum blood flow and nutrients to the placenta and enhances
kidney function, which means better elimination of waste products and less swelling in your feet, ankles and hands.
Keep pillows behind your back and between legs for more comfortable feel.. Or you can choose pregnancy pillow..