It's bad when you start felling uncomfortable in that position otherwise it doesn't affect you. The baby is still to small.
That's exactly what I went through . It's all up to how comfortable you are I do believe. I'm six months and don't sleep on my stomach anymore, I sleep on my side but still somewhat on my stomach .
I'm 34 weeks and still sleep on my stomach and sides of my stomach. Have never been able to sleep any other way since I was a kid. I do wrap my body pillow around my belly to lessen pressure on my belly.