Try sleeping with a pillow behind you. That way if you tend to roll over it'll be half way on one side or the other. It's not good to be on your back for a long period of time. Cuts oxygen off to the baby or slows the heart beat. I do the same thing. Always tend to wake up on my back. I got a body pillow as opposed to a maternity pillow. It was only 10.00 and it helps a lot. Which ever way I fall asleep, the pillow goes toward my back.
If that doesn't help you, sleep propped up with a lot of pillows. That tends to help me too when I can't get comfortable. I'm 34w5d so I know the feeling. It'll only get worse lol...
If it gets too bad, talk to your doctor about other ways to help you sleep better so you don't wake up on your back and be able to breathe.
I am 33 weeks as well' I think that since your baby is still growing your lungs don't have much room wich makes it twice as hard for us preggos to breathe. I am feeling the same way u r. But if it gets to the point where u can't take it I would call your ob.