best time to do a preg test???

Hi guys 
​Im kind of freaking out. My last period was aug 27th... And i still dont have my period yet.... Also usually a week before my period's start day i get backaches and reallyyyyy bad cramps but right now... Absolutely noooothiiinggg....should i do a preg test now? I mean those stick things? 
​Oh my god totallyyyy freaking out