As long as it's still comfortable for you everything should be okay. The only way I could fall asleep was on my stomach but to break my habbit I sleep on my side with a pillow between my legs to keep me from rolling over on my tummy.
And btw I'm 18wks my bf hates when I sleep on my tummy but I still do it sometime s
My doc told me that as long as im comfy on my stomach I can sleep on it until my body decides that I can anymore. I had a friend who was pregnant and she said she sleeps on her tummy rite up and nothing bad happen to she and her baby