AF came 7 days early??? Abnormal

Okay so I've been a little frustrated lately, well let's be honest, I've been the last 2 years ttc. On average since I was 11 my cycles have always been regular 31-33 days until this month when my period came out of the blue no warning signs 7 days early!!!! I almost always get the slight cramping, sore boobs and even sore back warning me AF is arriving any time. I just had my cycle 21 days ago. The bleeding is very very light. Is this normal or has happened to anyone else?! Nothing in my daily routine has changed.