Loss of oxygen at 37 wks 4 days

I’ve been trying to go to sleep for the past hour and as soon as I feel that I’m getting into that deep sleep, I wake up gasping for air as if I had no oxygen. It happened 5 times now. I tried sleeping on my right and left side and I still feel like I’m losing air. I added more pillows to keep my upper body elevated to see if that would help and it doesn’t. Only thing that helps is me sitting down. My oxygen goes down to 91 as soon as I lie down. What’s going on? Does anyone know what I should do?