Sleeping on tummy

Yes it’s okay! In fact in 2nd tri as well as Long as your tummy is still not big. You’ll know when it feels uncomfortable to lie on your tummy. Just don’t do it all the time. Cause you’re literally pressing on your tummy aka uterus with all that weight. But please start sleeping on your side (preferably left) as it gives maximum blood flow and nutrients to the placenta as your pregnancy progresses.