9 days post op of Breast Augmentation, when can I start sleeping flat on my back rather than propped up at 45 degree angle?

I got my breasts augmented 9 days ago, and the whole sleeping at a 45 degree angle, basically sitting up, is really starting to take its tole on my neck and back. I'm so uncomfortable that I wake up so many times during the night trying to reposition pillows and such. I know my plastic surgeon will give me the ok to sleep on my sides at some point, but when can I lay down without being propped up???