I know most health professionals would advise not to sleep on tummy. They also advise not to sleep on your back as this puts too much pressure on as the baby gets bigger. Its suggested that sleeping on your sides are better as the pregnancy progresses, but i often wake up finding myself sleeping on my back still. However, having said that i do suffer from back pain a lot already and SPD, so sleeping on my back might have something to do with making it worse lol.
Have you tried a couple of pillows to keep you on your side in a comfortable way? Or maybe even a pregnancy pillow? I have a maternity one and it does help take the weight off my bump when i lay on my tummy, which helps a lot. I think at this stage i would personally find sleeping on my tummy really uncomfortable although i am further along then you are.