Age 31,last Month Had My Periods On 2nd July, We

age 31,last month had my periods on 2nd july, we always have protective relation. pregnancy test done on 7th Aug,it is negative.still havn't gt my period. so what could be the reason.Still how many days to wait. I am married. mostly periods are 30days cycle but sometimes get delayed. i was under stress from past 15 days