I would just add that you can sleep on you back if you feel comfortable. Once you get further along you can back sleep with a pillow or a rolled up towel under your right side so that you're slightly tilted. 😉

yes, don't lay on your back. it puts pressure on your spine and a major artery and reduces blood flow to the uterus and your lower extremities. left side is best to lay, right side is ok, stomach is ok if it's comfortable. when it's not comfortable anymore, start laying on your sides.

Since im a stomach sleeper, my dr told me to lay in any position comfortable for you and you won't squish the baby. it's not recommended to sleep flat on your back is all :)