Why would I be so late after an early miscarriage?

I'm on cycle day 40 with no symptoms of AF or pregnancy. took hpt this morning and it was neg. My hsg was at 0 early last week when we did beta and my beta only ever got up to 47.4 at 4 weeks. I had another m/c at same gestation in Dec and my cycle went right back to normal after that. Why no AF or BFP?