My 15 weeks old daughter sleeps on her front!!!?

I have been adviced about the cot death. My 15 weeks old daughter sleeps on her front since she was 6 weeks old as she will not sleep on her back. when she was born we didnt know why she was crying but she wouldnt sleep at all. So when she was 6 weeks old, i turned her on her front one day and she slept very comfortably. My mum told me that me and my brother use to sleep like that too. Midwifes told me not to, and adviced me to try lots of different thing, like putting her in a car seat at night or in her bouncer. None of that worked for her, she cries untill i take her and put her on her front.