Period late BFN

Been taking tests every two days since 8 dpo. Was negative 8dpo, 10 dpo, and again this morning which is 13 dpo and my period is supposed to start. Still haven't gotten my period and no normal signs of starting it but no pregnancy signs either. I bought a more expensive test to take in the morning but has this happened to anyone else? I ALWAYS get my period 13 dpo and its late but I'm getting nothing not even a faint line. Help!