I haven't gotten preggers since the MC (yet) but my ob said the reason you are more fertile in the first few months after the MC is because you have a soft cervix and increased blood flow. It is perfect conditions for implantation.
I just went to the loo and there is blood (not brown but pinky red) like the start of my af! I also have the feeling in my stomach that its started. Thank God as now i can move on.