I reread Dany's last chapter. It stuck out to me that it is left a bit ambiguous whether or not she has the plague, but that she is fertile again. You know that old Mirri Maz Duur prophecy that Dany keeps thinking about - "When the sun rises in the west and sets in the east. When the seas go dry and mountains blow in the wind like leaves. When your womb quickens again, and you bear a living child. Then he will return, and not before."
Perhaps the blood is her womb quickening again. Dany did have trouble remembering when her last period was. So Quentyn could be the sun that rose in the west and set in the east. The seas going dry. Sure I can't think of how the seas have gone dry (besides the fact that the Dothraki sea is grass...), but can't think about how the mountains have blown in the wind. Anyways something more to think about over the next few years while GRRM writes the next book.