Period

So first glow tells me my AF was due the 11th and it never showed so I tested and got a BFN now it's telling me that it's actually due tomorrow.... Has anyone else ever seen their dates change? I'm also trying to figure out why I can have a 28 day cycle my whole life then all of the sudden I'm on a 38 day cycle. To me it's one thing to go from a 28 to a 30 maybe even 32 day cycle one month due to late ovulation but a whole 10 days? I find that hard to believe.