Sleeping on back?

I’m almost 30 weeks and I’ve had terrible SPD since week 16. My OB didn’t care if I slept on my back through second trimester. Now that I’m in third, her office midwife (I met with her instead most recently, only because of availability) told me not to sleep on my back anymore. But because of the SPD I can only stay on my side for 5-10 minutes before I’m in pain 😫 I don’t get tingly or lightheaded or anything from being on my back - so shouldn’t it be fine?

Personal experience???