Sleep On Left Or Right?

Lately I've been having fast heartbeat and alil shortness of breath. I know sleeping on the left is better for baby but wouldn't I be adding more pressure on my heart? Bcz before pregnant, I'd sleep on my right as i learnt that it is better for the heart. I feel that i cn breathe better when sleeping on my right but am worried that baby is not getting enough oxygen. Im currently 4 mths pregnant.