Hello NK,
I'm so sorry to hear this. The same thing happened to me last April. The pregnancy had been progressing well (chronic morning sickness right up until the end unfortunately). Our baby girl was the right size for dates, and we weren't offered a post mortem, however the chromosome tests came back completely normal, so we will never know why her heart stopped beating.
All I can say is that you need to give yourself time to grieve. The next pregnancy is tough, especially the first half (I am now 30 weeks), because you have lost the innocence in some ways.
I was told again and again that it is extremely unlikely that this would happen twice - especially if there is no reason found from the post mortem. There is also absoloutely no reason for you to take longer to conceive this time round.
My advice would be to look after yourself, and allow yourself time to come to terms with the bereavement.
Getting pregnant again did help me, however, I certainly didn't have the (mental) strength to do it again straight away (we had a 5 month gap between losing our first baby and conceiving the second). It is still early days for you - less than a month since this terrible shock, so don't feel you have to rush in to anything. Alternatively, you may feel that you need to be pregnant again for your own sake. Everyone is different.
I hope that helps. The moment in the scanning room, I think, will stay with us forever, but the pain does recede with time.