I am 30 weeks and still sleep partically on my stomach. It is the only way I get any sleep. Once you get bigger you may find something more comfortable or you can use a pillow in between you and the matress like a wedge.
I was still sleeping on my stomach at 17wks. I asked my Ob and he said I was fine as long as it was comfortable for me. No ur not hurting baby. Your body will know when it cannot tolerate u being on your stomach and soon enough u will be too big and it will become to uncomfortable to do so anyways.
Congrats on your pregnancy and good luck!!