I think it happens different for everyone. After my D&C I counted the D&C as CD1, spotted from the D&C until about CD20, ovulated on CD25, and AF showed on CD41. But my HCG level was at 24 when AF came. So it is possible to still have some of the hormones left after AF (but that could just be because I had a molar pregnancy?) During my AF I also passed some larger clots than normal - maybe passing the rest of the tissue? Not sure if that actually answers your questions or not but that was how it happened for me