31 weeks 2 days BLEEDING

So was only the other day I was upset over my mum losing her baby at 10 weeks but she didn't know till 12 weeks, now here I am in hospital because I woke up in the morning blood all over pillow and on the sheets was dried but still dark red blood so must of happened early morning and when I went to the loo most the blood came out in the loo. I honestly was so worried first thing I did was get the dopler out and check to see if I could hear her which I could, then called partner but the midwife called for ambulance for me... now I have to stay in Over night, I have scan tomorrow as my last scan at 20 weeks I did have a low placenta so who knows why I was bleeding they checked my womb and it was closed but anything could happen over night... has anyone experienced bleeding like a period and then hours and hours later went into early labour or even had to have a c section due to placenta playing up