Glow changed my period prediction

So all along the app said my period was due 1/20. Then when i input a recent bbt it changed my prediction to 1/26. And now it moved all the fertile window days from this month. I’ve never had this happen before. Has anyone else? I’m hoping we finally succeeded this month after about a year of trying! I have all period like symptoms which could be early pregnancy symptoms. Not sure when I should take a pregnancy test though since the app changed my predicted period date. The app has always predicted pretty close to accurate these past few months. Just wondering why it would change the date after almost a month of inputting BBTs