Most pregnat women with low risk pregnancies will not need, or have an ultrasound after 20 weeks. They can tell by feeling. Usually my OB find the heartbeat first then she knows where the upper half is and feels from there. I have never had a breech baby, but I have a friend who has. When she was 36 weeks her doctor started talk of inversion, they kept an eye on it, baby never flipped, she had a csection at 39 weeks. I am sure different providers do different things.
This, my doctor can tell with the heart beat and feeling around. 31 weeks is a little early to worry about which direction baby is facing. Most insurance companies will not cover an extra u/s unless there is a medical need.