Well, month three has gone by with no sign of baby #5. My friendly "Aunt Flo" has made her appearance.
This is very different for us. This trying and trying with no baby. Two of our four were unplanned surprises and the other two were something like, "Hey, do you think that we should start trying to have a...we're pregnant!")
So, I don't know why it isn't happening, but there is obviously a reason. Maybe one day I will figure out what that is. For now, I'll have to settle for being frustrated.