Sleeping on your tummy....

Joy
Hi ladies, I'm 15 weeks pregnant and I find myself sleeping on my stomach every night and it doesn't hurt........... Kinda worried over here.... I'm pregnant with my 1st...... Don't know if that's normal.... I know the baby is small but is it normal, until how many months (normally) can you not sleep on your stomach? 
I'm slightly showing not much tho....