It is not compulsory to sleep only on the left side. Left side sleeping is preferred in later pregnancy(term pregnancy) as it helps blood flow to the baby and reduces pressure on major blood vessels. However, sleeping on the right side is also safe and fine if that is more comfortable for you. But, avoid lying flat on your back for long in the last trimester.
Next Steps
Continue sleeping on the side that is most comfortable. If you feel breathlessness, dizziness, numbness, or decreased baby movements with any of the position, consult gynaecologist immediately.
Health Tips
Can place pillows behind the back and between the knees which can improve comfort. Try to avoid prolonged sleeping in supine position especially in late pregnancy.