Okay, I don't mean to sound stupid or ignorant but I'm extremely new to this fertility tracking idea and I'm trying to educate myself on everything involved but there's something that's got me a little confused. I noticed on my glow calendar that my fertile (or ovulation) dates were set for a certain range and then BOOM all of a sudden those dates shifted on me on Friday and it looks like my "window of opportunity", so to speak, passed me by apparently on Friday when it shouldn't have been until around the 27th. Why does my fertility/ovulation dates just change like that??