I'm 8 months pregnant and still sleep on my back(flat) it's mostly bad for you than the bad cause of pressure the baby puts on things in your body. And my doc hasn't said anything about it

@maybabyboy, it sucked having to sleep propped up but it had many benefits when I got further along. Les likely to get heartburn at night and my hips/legs didn't hurt as bad when I woke up. if I slept on my side my boyfriend would have to help me get out of bed and help me walk a little to help ease the pain. .

Like @andiryan93 said, there are things you can do so it's not so bad.

after the 1st trimester

I don't remember what my midwife said but I was also told if you are propped up you can semi lay on your bed. the last couple of months in my pregnancy with my daughter I had to sleep propped up because I couldn't lay on my sides bc it would cause me so much pain in my legs.